dt-bindings: input: Add compatible string for SC2721 and SC2730

Add new compatible strings to support sc2730 and sc2721 which are
two varieties of SC27XX family.

Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201117034949.47877-4-zhang.lyra@gmail.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>