drm/amd/display: Reset alpha state for planes to the correct values
[Why]
The plane_reset callback is subclassed but hasn't been updated since
the drm helper got updated to include resetting alpha related state
(state->alpha and state->pixel_blend_mode). The overlay planes
exposed by amdgpu_dm were therefore being rendered as invisible by
default ever since supported was exposed for alpha blending properties
on overlays.
This caused regressions in igt@kms_plane_multiple@atomic-tiling-none
and igt@kms_plane@plane-position-covered-pipe tests.
[How]
Reset the plane state values to their correct values as defined in
the drm helper.
This fixes the IGT test regression.
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com> Reviewed-by: Harry Wentland <Harry.Wentland@amd.com> Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>