drm/radeon: make all functions work with multiple rings.

Give all asic and radeon_ring_* functions a
radeon_cp parameter, so they know the ring to work with.

Signed-off-by: Christian König <deathsimple@vodafone.de>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>