dt-bindings: display: simple: add Geekworm MZP280 Panel

The Geekworm MZP280 panel is a 480x640 (portrait) panel with a
capacitive touch interface and a 40 pin header meant to interface
directly with the Raspberry Pi. The screen is 2.8 inches diagonally,
and there appear to be at least 4 distinct versions all with the same
panel timings.

Timings were derived from drivers posted on the github located here:
https://github.com/tianyoujian/MZDPI/tree/master/vga

Additional details about this panel family can be found here:
https://wiki.geekworm.com/2.8_inch_Touch_Screen_for_Pi_zero



Signed-off-by: Chris Morgan <macromorgan@hotmail.com>