msm: mdss: Add support for DSPP3 in histogram interrupt handler

Previously, we weren't handling histogram done interrupts for DSPP3 in
the interrupt handler. The handler now looks to handle those interrupts.
A helper function to parse the interrupt mask has been added to return
the correct histogram info block.

Change-Id: Ie469a4030b4f4f7ee8e4b8a766539c43f87504ac
Signed-off-by: Benet Clark <benetc@codeaurora.org>