drm/amd/display: Blank eDP on enable drv if odm enabled

[Why]
For panels with pixel clock > 1200MHz that require ODM
in pre-OS, when driver is disabled in OS, odm is enabled.
Upon driver enablement, corruption is seen if
odm was originally enabled. DP_PIXEL_COMBINE and
pixelclk must be programmed prior to programming the
optc-odm registers. However, eDP displays aren't blanked
prior to initializing odm in this case.

[How]
Upon driver enablement, check whether odm is enabled,
if so, blank eDP prior to programming optc-odm
registers.

Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Duncan Ma <duncan.ma@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>