msm_fb: display: Configure DMA before Layer Mixer for writeback mode switch

DMA addresses are configured after Layer Mixer is set to writeback mode.
This leads to IOMMU page faults due to incorrect addresses read from DMA.
Hence DMA is programmed before Mixer setting.

Change-Id: I4c5e41a56f05e3fabb46b4cadde03168589eeb17
Signed-off-by: Ravishangar Kalyanam <rkalya@codeaurora.org>