drm/amd/display: add condition check for dmub notification

[Why & How]
In order to have dc_enable_dmub_notifications() more precise, add
one more condition to check if dc->debug.dpia_debug.bits.disable_dpia
is false.

Signed-off-by: Meenakshikumar Somasundaram <meenakshikumar.somasundaram@amd.com>
Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>