dt-bindings: arm: Add bindings for SP9860G

Added bindings for Spreadtrum SP9860G board and SC9860 SoC.
This patch also revised bindings of SC9836 to make the format
more clear.

Signed-off-by: Chunyan Zhang <chunyan.zhang@spreadtrum.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>