drm/amd/display: change FIFO reset condition to embedded display only

[Why]
FIFO reset is only necessary for fast boot sequence, where otg is disabled
and dig fe is enabled when changing dispclk. Fast boot is only enabled
on embedded displays.

[How]
Change FIFO reset condition to "embedded display only".

Signed-off-by: Zhan Liu <zhan.liu@amd.com>
Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>