board-msm7627a: Display: Add support for shared GPIO

Add support for voltage regulators VEXT_2V8 and VEXT_1V8 through
regulator apis and remove gpio apis for the same as the same gpios
are used by camera.

CRs-Fixed: 354986
Change-Id: I5b3ae2c8fb62a05fdbe8582e5dcb6a2b07f0b31a
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>
Signed-off-by: Raju P.L.S.S.S.N <rplsssn@codeaurora.org>