drm/amd/display: Interfaces for hubp blank and soft reset

[WHY]
HUBP blanking sequence on DCN30 requires us to check if HUBP is in blank
and also toggle HUBP_DISABLE, which should instead be called
HUBP_SOFT_RESET for what it does in HW.

Signed-off-by: Wesley Chalmers <Wesley.Chalmers@amd.com>
Acked-by: Bindu Ramamurthy <bindu.r@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>