drm/amd/display: Speed up DML fast_validate path

[Why]
Iterating over every voltage state when we need to validate thousands of
configurations all at once (i.e. display hotplug) can take a significant
amount of time.

[How]
Check just the highest voltage state when fast_validate is true to
verify whether the configuration can work at all, then do a proper
validation including all voltage states later when fast_validate is false.

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Jasdeep Dhillon <jdhillon@amd.com>
Signed-off-by: Ilya Bakoulin <Ilya.Bakoulin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>