msm_fb: Remove the extra freelist in display_commit

There is an extra freelist call to unmap IOMMU source buffers
in display_commit for LCDC interface. This is causing IOMMU
page faults during boot up on targets with LCDC interfaces.
Remove this extra freelist call.

Change-Id: I12a905efc82c5b9751acbc5941a66d0b58027509
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>
msm_fb: display: Do a pre-fill to writeback buffers.

When switching mdp operating mode to blt, writeback buffers need
pre-fill. Move the pre-fill code from isr routine to do_blt, where
actual switch to blt mode happens.

CRs-fixed: 471098
Change-Id: I0f845397894c749ac518a1fa605f84cd5fc2ad15
Signed-off-by: Mayank Chopra <makchopra@codeaurora.org>

Conflicts:
	drivers/video/msm/mdp4_overlay_dsi_video.c

Signed-off-by: Rohan Mathur <rohanmathur34@gmail.com>