msm: mdss: make panel status check and dfps update exclusive

Since on some platforms DSI_CMD_OFFSET register has become
double buffered, so dynamic fps update and DSI DMA command
transfer can not happen at the same time. This changes makes
panel status check which in turn does a DSI DMA transfer, and
dfps update mutually exclusive.

Change-Id: If8591c55d31669dbf3f565db041c04bcd6cb616a
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>