disp: msm: dsi: handle wait for dma cmd completion

The current solution triggers the DMA command and waits till
the command dma done and ISR signals completion. This change
introduces asynchronous wait after a DCS command has been
triggered. Enable this mode only during pre kickoff, so as to not
block commit thread.

Change-Id: Iead7b6328883e844147d47ff68dc878943879553
Signed-off-by: Satya Rama Aditya Pinapala <psraditya30@codeaurora.org>