msm: mdss: add support for DMA TPG for sending panel commands

Currently, the DSI controller fetches DMA commands through the
MDP VBIF interface. The DMA data is fetched from memory only
when software triggers command DMA. The latency might be long
between fetches. A FIFO is present in the DSI controller to
bypass the VBIF interface from DSI rev 1.3.0. The user can
pre-fill the DMA data in the FIFO via the AHB bus before
triggering the command DMA operation. Add support for this.

CRs-fixed: 873962
Change-Id: Ieff7575fa4483c87e3b3665149f313828d9b09a7
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>
[veeras@codeaurora.org: Resolve conflicts in mdss_dsi_host.c]
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>