vmwgfx: Implement memory accounting for resources

Contexts, surfaces and streams allocate persistent kernel memory as the
direct result of user-space requests. Make sure this memory is
accounted as graphics memory, to avoid DOS vulnerabilities.

Also take the TTM read lock around resource creation to block
switched-out dri clients from allocating resources.

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