drm/amdgpu: drop redundant cg/pg ungate on runpm enter

CG/PG ungate is already performed in ip_suspend_phase1. Otherwise,
the CG/PG ungate will be performed twice. That will cause gfxoff
disablement is performed twice also on runpm enter while gfxoff
enablemnt once on rump exit. That will put gfxoff into disabled
state.

Fixes: b2a7e973

 ("drm/amdgpu: fix the hw hang during perform system reboot and reset")
Signed-off-by: Evan Quan <evan.quan@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org