drm/vmwgfx: Fix a couple of compile / sparse warnings and errors

Fixes
 *) an implicit function declaration on mips,
 *) a defined but not used label on !CONFIG_INTEL_IOMMU
 *) Hopefully a couple of sparse warnings where we implicitly typecast
    integer to __le32 and vice versa.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>