drm/amd/powerplay: Enable/Disable NBPSTATE on On/OFF of UVD

We observe black lines (underflow) on display when playing a
4K video with UVD. On Disabling Low memory P state this issue is
not seen.
Multiple runs of power measurement shows no imapct.

Signed-off-by: Akshu Agrawal <akshu.agrawal@amd.com>
Signed-off-by: Satyajit Sahu <satyajit.sahu@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org