msm: mdss: update the dsi interrupt handling on 8x10

The previous dsi interrupt handling logic was scattered
in a few places.  This is to centralize the interrupt
handling logic.

Change-Id: If89a45d80a2e3523368a37d96f1d226c443e1f61
Signed-off-by: Xiaoming Zhou <zhoux@codeaurora.org>