[PATCH] ARM64: meson-gxbb-p200: add ADC laddered keys

Neil Armstrong [off-list ref] writes:

Add the 5 buttons connected to a resistor laddered matrix and sampled
by the SAR ADC channel 0.

Only the p200 board has these buttons, the P201 doesn't.

Signed-off-by: Neil Armstrong <redacted>

Applied to v4.11/dt64.

Note that I fixed up the subject prefix to be ARM64: dts:

Kevin