drm/msm/dsi-staging: enable interrupt support

Enable basic interrupt support for DSI driver. A generic ISR is
provided within dsi_ctrl that clears status interrupts; each
individual DSI status interrupt may be enabled/disabled from the
rest of the DSI driver via a provided API function.

CRs-Fixed: 2027542
Change-Id: I2645b9e705fa03e18a584e0ee04c05f6c1ce787e
Signed-off-by: Clarence Ip <cip@codeaurora.org>
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>