drm/amd/display: keep eDP Vdd on when eDP stream is already enabled

[Why]
Even if can_apply_edp_fast_boot is set to 1 at boot, this flag will
be cleared to 0 at S3 resume.

[How]
Keep eDP Vdd on when eDP stream is already enabled.

Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Jasdeep Dhillon <jdhillon@amd.com>
Signed-off-by: Zhan Liu <Zhan.Liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>