drm/radeon: add set_uvd_clocks callback for r7xx v3

v2: avoid 64bit divide
v3: rv740 uses the evegreen upll configuration

Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>