drm/amdgpu: Add dcdebugmask option to enable DPIA trace

drm/amdgpu: Add dcdebugmask option to enable DPIA trace

[Why & How]
It's useful to be able to enable DPIA trace with dcdebugmask
option, especially to debug DPIA issues involved in transition
of system power states.

This patch adds an option to amdgpu.dcdebugmask to be picked up
by amdgpu DM to enable DPIA trace.

Signed-off-by: Stylon Wang <stylon.wang@amd.com>
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>