drm/radeon/kms: do bounds checking for 3D_LOAD_VBPNTR and bump array limit

drm/radeon/kms: do bounds checking for 3D_LOAD_VBPNTR and bump array limit

commit a27bb4b209dd6c327fa4e7185f2487f9508a58db upstream.

To my knowledge, the limit is 16 on r300.
(the docs don't say what the limit is)

The lack of bounds checking can be abused to do all sorts of things
(from bypassing parts of the CS checker to crashing the kernel).

Bugzilla:
https://bugs.freedesktop.org/show_bug.cgi?id=36745

Signed-off-by: Marek Olšák <maraeo@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>