drm/amd/display: send pipe set command to dmcu when stream unblanks

[Why]
When stream is blanked, pipe set command is sent to dmcu to notify it
that the abm pipe is disabled. When stream is unblanked, no notification is
made to dmcu that the abm pipe has been enabled, resulting in abm not
being enabled in the firmware.

[How]
When stream is unblanked, send a pipe set command to dmcu.

Signed-off-by: Josip Pavic <Josip.Pavic@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>