msm: add display bridge abstraction driver

Add display bridge abstraction driver to provide an abstract interface
for different types of bridge chips used on MSM platforms. This
interface allows driver development for bridge chips from different
manufactorers while allowing users, of the funcationality provided by
these bridge chips, to re-use the same code across different boards.

Change-Id: I64457e3a44479a3b1be5482691d4727a86dc9b87
Signed-off-by: Vinu Deokaran <vinud@codeaurora.org>
Signed-off-by: Siddharth Zaveri <szaveri@codeaurora.org>