drm/amd/display: Clear GPINT after DMCUB has reset

[Why]
Otherwise we can end up processing whatever was left in the register
if the DMCUB was previously reset.

If DMCUB gets force reset too early from another client then we might
not have even acked the disable yet - causing DMCUB instantly shutdown
if the command was 10020000.

[How]
Move the GPINT clear outside of the reset loop and do it unconditionally
after the DMCUB has been properly reset.

Reviewed-by: Roy Chan <roy.chan@amd.com>
Reviewed-by: Eric Yang <Eric.Yang2@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>