dts: add overlay for pitft22

Add the pitft22 overlay from adafruit Adafruit-Pi-Kernel-o-Matic repo:
https://github.com/adafruit/Adafruit-Pi-Kernel-o-Matic



Signed-off-by: Petter Mabäcker <petter@technux.se>
Signed-off-by: Andrei Gherzan <andrei@resin.io>