drm/radeon/kms: Add support for multi-ring sync in CS ioctl (v2)

Use semaphores to sync buffers across rings in the CS
ioctl.  Add a reloc flag to allow userspace to skip
sync for buffers.

agd5f: port to latest CS ioctl changes.

v2: add ring lock/unlock to make sure changes hit the ring.

Signed-off-by: Christian König <deathsimple@vodafone.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>