socinfo: Add of_board_is_cdp API

Some targets need to choose the board-specific
config data at run-time and hence this API is required.
E.g. gpiomux_install for a gpio that is used differently
on a CDP vs other boards.

Change-Id: I80b3f7f7c52ab0beadfd14d91536289f331ca08d
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>