Document board compatible names for Pine64 PinePhone:

- 1.0 - Developer variant
- 1.1 - Braveheart variant
Signed-off-by: Ondrej Jirman <megous@megous.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>