drm/radeon/kms: bogus cs recorder utilities

This add an utilities function radeon_ib_bogus_add which will
save an ib into a list of ib which can then be dumped using
debugfs. Once dumped the ib is removed from the list. This
should allow to save & capute ib for further debugging.

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>