Add support for EastRising (BuyDisplay) ER-OLEDM1602-4Y

[rfmerrill]

This is a small change but took a while of banging on it to get it to work.

The ER-OLEDM1602-4Y is much easier to acquire than the WinStar display in the US, and cheaper as well.

The required changes are:

• Repurpose the blinking LED pin for the RESET line to the display, as it does not seem to have a good POR circuit built in.
• Slightly different initialization sequence (E starts low, no command required to put it in 4-bit mode, can skip the multiple 0 writes.)
• Hack around the controller putting the second line at 0x20 instead of 0x40 (note: The display controller datasheet says it should be at 0x40 but I could only get it to work at 0x20).

The display has three solder jumpers BS0-BS2, they should be HIGH LOW HIGH for 4-bit 6800 mode.

The wiring is as follows:

• E connects to the pin labeled RD
• RS connects to the pin labeled DC
• PB1 connects to the pin labeled RES
• CS should be tied to ground
• VCC should be 3.3V
• The rest of the pins (D4-D7, RW, and GND) connect as normal.

Note also that this display appears to be upside-down relative to the Winstar and Adafruit ones.