drivers/Makefile.dep: remove inappropriate use of FEATURES_PROVIDED for rtt_rtc

[aabadie]

Contribution description

As seen when reviewing #14496, there's no reason to use FEATURES_PROVIDED in a Makefile.dep. The dependency resolution can be done later.
Any cpu already providing periph_rtt but not periph_rtc could simply add:

ifneq (,$(filter periph_rtc,$(USEMODULE)))
  USEMODULE += rtt_rtc
endif

in its Makefile.dep and add

FEATURES_PROVIDED += periph_rtc

in its Makefile.features

and that would work.

Maybe this breaks other platforms, let's see what Murdock has to say.

Testing procedure

Test periph_rtc on nrf5x platforms with #14496 and it'll still work.

Issues/PRs references

Found while reviewing #14496

[benpicco]

Ok with this line removed, #14496 becomes necessary.

% make BOARD=nrf52840dk -C tests/periph_rtc 
make: Entering directory '/home/benpicco/dev/RIOT/tests/periph_rtc'
There are unsatisfied feature requirements: periph_rtc
/home/benpicco/dev/RIOT/tests/periph_rtc/../../Makefile.include:886: *** You can let the build continue on expected errors by setting CONTINUE_ON_EXPECTED_ERRORS=1 to the command line.  Stop.
make: Leaving directory '/home/benpicco/dev/RIOT/tests/periph_rtc'

whereas on master

% make BOARD=nrf52840dk -C tests/periph_rtc
make: Entering directory '/home/benpicco/dev/RIOT/tests/periph_rtc'
Building application "tests_periph_rtc" for "nrf52840dk" with MCU "nrf52".

"make" -C /home/benpicco/dev/RIOT/boards/nrf52840dk
"make" -C /home/benpicco/dev/RIOT/boards/common/nrf52xxxdk
"make" -C /home/benpicco/dev/RIOT/core
"make" -C /home/benpicco/dev/RIOT/cpu/nrf52
"make" -C /home/benpicco/dev/RIOT/cpu/cortexm_common
"make" -C /home/benpicco/dev/RIOT/cpu/cortexm_common/periph
"make" -C /home/benpicco/dev/RIOT/cpu/nrf52/periph
"make" -C /home/benpicco/dev/RIOT/cpu/nrf5x_common
"make" -C /home/benpicco/dev/RIOT/cpu/nrf5x_common/periph
"make" -C /home/benpicco/dev/RIOT/drivers
"make" -C /home/benpicco/dev/RIOT/drivers/periph_common
"make" -C /home/benpicco/dev/RIOT/drivers/rtt_rtc
"make" -C /home/benpicco/dev/RIOT/sys
"make" -C /home/benpicco/dev/RIOT/sys/auto_init
"make" -C /home/benpicco/dev/RIOT/sys/div
"make" -C /home/benpicco/dev/RIOT/sys/isrpipe
"make" -C /home/benpicco/dev/RIOT/sys/newlib_syscalls_default
"make" -C /home/benpicco/dev/RIOT/sys/stdio_uart
"make" -C /home/benpicco/dev/RIOT/sys/test_utils/interactive_sync
"make" -C /home/benpicco/dev/RIOT/sys/tsrb
"make" -C /home/benpicco/dev/RIOT/sys/xtimer
   text	   data	    bss	    dec	    hex	filename
  14264	    128	   2448	  16840	   41c8	/home/benpicco/dev/RIOT/tests/periph_rtc/bin/nrf52840dk/tests_periph_rtc.elf

[aabadie]

There are unsatisfied feature requirements: periph_rtc

And this is normal since the cpu doesn't provide that feature.

[aabadie]

If one wants to use the RTT emulated RTC then just add USEMODULE += rtt_rtc in the application Makefile.

[benpicco]

If you want I can also include this commit in #14496

[benpicco]

If the feature is provided by the board / CPU, this is not needed here.

[fjmolinas]

@aabadie what is this PR waiting for?

[benpicco]

I added the label because IMHO we should merge #14496 first to not lose the functionality.
Then there was disagreement if we should have this by default in the first place.

I wanted RTC emulation enabled automatically for targets that only have a RTT, but @aabadie noted that a user could then also call rtt_ functions without a warning which would mess with the RTC emulation / RTC emulation would mess with the behavior of RTT.

[aabadie]

what is this PR waiting for?

Normally, nothing. if @benpicco agrees, we can (not to say should) remove the label.

[fjmolinas]

#14496 Has some issues regarding integration with our current build system, lets go ahead with this one as is.

[benpicco]

We could at least have left this in place, it's only used if periph_rtc is explicitly requested.

[aabadie]

It makes no sense if the board doesn't provide that feature.