drm/amd/display: Send IPSExit unconditionally.

[Why&How]
PMFW needs to flush page cache in IPSExit.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: JinZe Xu <JinZe.Xu@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>