msm: mdss: Add support for SRGB IGC

Inverse gamma correction(IGC) linearizes the incoming pixels of a layer
before blending it with other layers. Change adds support for sRGB
format.

Change-Id: I2b30adeae5a10354f485c8e78c9d8c938e1ccf1f
Signed-off-by: Gopikrishnaiah Anandan <agopik@codeaurora.org>