drivers: counter: migrate counter AGT to using HAL support

Migrate renesas,ra-agt-counter implementation to use hal_renesas.
Add additional AGT_CLOCK_SUBCLOCK count source.
Add constraint for counter resolution to 32 or 16 bit variant.

Signed-off-by: The Nguyen <the.nguyen.yf@renesas.com>

Author: thenguyenyf

drivers/counter/Kconfig.renesas_ra

@@ -7,5 +7,6 @@ config COUNTER_RA_AGT
 	bool "Renesas RA AGT driver"
 	default y
 	depends on DT_HAS_RENESAS_RA_AGT_COUNTER_ENABLED
+	select USE_RA_FSP_AGT
 	help
 	  Enable support for Renesas Low Power Asynchronous General Purpose Timer (AGT) driver.