This interface allows userspace to request hyperz support, it probably
needs more locking, and really reporting that you can have hyperz is racy
since someone else might get it before you do.

v2: modify so we pass 0 valued packets to let DDX/r300c keep working.
also fixed incorrect 0x4f1c reference.

v3: fixup zb_bw_cntl so older drivers keep working

v4: add locking, fixup SC_HYPERZ_EN - patch stream to disable hiz
Signed-off-by: Dave Airlie <airlied@redhat.com>