msm: mdss: handle DSI error interrupts during dynamic fps

During dynamic fps using PLL approach, it is expected that DSI
FIFO underflow and DSI PLL unlock can happen sometimes. Make sure
to mask these errors so that DSI error interrupt is not generated
because of this. Clear the errors once dynamic refresh operation
is done and unmask these errors later.

Change-Id: I05ccbb7af1588b9ed81fd33ac14ef5b29882a42d
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>