arm64: allwinner: dts: pinephone: add 'pine64, pinephone' to the compatible list

All revisions of the PinePhone share most of the hardware.
This patch makes it easier to detect PinePhone hardware without
having to check for each possible revision.

Signed-off-by: Dylan Van Assche <me@dylanvanassche.be>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20201230104205.5592-1-me@dylanvanassche.be