arm64: dts: allwinner: pinephone: Add LED flash

All revisions of the PinePhone have an SGM3140 LED flash. The gpios were
swapped on v1.0 of the board, but this was fixed in later revisions.

Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20201105054135.24860-4-samuel@sholland.org