drm/msm/dpu: Clean up dpu hw interrupts

Remove unused functions and macros from files handling
dpu hardware interrupts.

changes in v2:
  Removed clear_interrupt_status (Jordan Crouse)
changes in v3:
  Changed commit text

Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>