drm/amdgpu: correct the wrong cached state for GMC on PICASSO

Pair the operations did in GMC ->hw_init and ->hw_fini. That
can help to maintain correct cached state for GMC and avoid
unintention gate operation dropping due to wrong cached state.

BugLink: https://gitlab.freedesktop.org/drm/amd/-/issues/1828



Signed-off-by: Evan Quan <evan.quan@amd.com>
Acked-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>