drm/amd/display: Call DMUB for eDP power control

[Why]
If DMUB is used, LVTMA VBIOS call can be used to control eDP instead
of tranditional transmitter control. Interface is agreed with VBIOS
for eDP to use this new path to program LVTMA registers.

[How]
Expose DAL interface to send DMUB command for LVTMA control that VBIOS
currently uses.

Signed-off-by: Chris Park <Chris.Park@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Eryk Brol <eryk.brol@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>