drm/radeon/si: add dpm quirk for Oland

OLAND 0x1002:0x6604 0x1028:0x066F 0x00 seems to have problems
with higher sclks.

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org