drm/msm/dp: fix handling of unsupported IRQ requests

Fix the handling of unsupported IRQ requests by making these
requests no-ops. This will prevent the DisplayPort driver
from entering into a loop in which the display is repeatedly
powered on unnecessarily.

CRs-Fixed: 2094794
Change-Id: I4eabfb6e50ac405a9ae1110841adc178822e0084
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>