drm/radeon/uvd: use lower clocks on old UVD to boot v2

Some RV7xx generation hardware crashes after you
raise the UVD clocks for the first time. Try to
avoid this by using the lower clocks to boot these.

Workaround for: https://bugzilla.kernel.org/show_bug.cgi?id=71891

v2: lower clocks on IB test as well

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