vmwgfx: Fix potential execbuf deadlocks

Perform all command stream validation in a bounce buffer separate from the
fifo. This makes the fifo available to all validation-generated commands,
which would otherwise attempt to grab the fifo recursively, causing a
deadlock. This is in preparation for GMR2 and swappable surfaces.

Also maintain references to all surfaces in the command stream until the
command stream has been fired in order to avoid racing with surface
destruction taking place after validation but before submission.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>