msm_fb: display: Consolidate commit ioctls

Overlay commit and display commit were two separate
ioctls doing similar things. This change consolidates
the two into one display commit ioctl. With this, we
can use the RGB0 pipe with an IOMMU framebuffer.

Change-Id: I2b51e16a6678e6cec1bd3e56a00a476addb1296f
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
Signed-off-by: Naseer Ahmed <naseer@codeaurora.org>