ARM: dts: s3: pinecube: align compatible property to other S3 boards

The compatible string in the Pine64 Pinecube dts diverges from the ones
used in other S3 based boards, like the LicheePi and the Elimo Impetus
and Initium. Discussion on LKML decided the PineCube should align to the
others.

Signed-off-by: Matteo Scordino <matteo.scordino@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20201030234325.5865-7-matteo.scordino@gmail.com