msm: mdss: update the MDSS DSI ULPS exit sequence

Add change to exit the DSI ULPS mode after enabling the DSI
escape clock and before enabling the DSI PLL. Check for the
DSI PLL unlock error bit and clear it before enabling the
DSI PLL to avoid false error interrupt after turning on
the PLL.

Change-Id: I53042fed9e4e45b64f75190abd4a295c0bc76baa
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>