i965: Make brw_bo_unmap a static inline.

i965: Make brw_bo_unmap a static inline.

With the broken debugging code gone, it doesn't do anything anymore.
We could technically eliminate it, but I'd like to keep it around in
case we want to add something there again someday.  Otherwise we'd
have to go all over the codebase adding unmap calls back again.

Based on a patch by Chris Wilson.

Reviewed-by: Matt Turner <mattst88@gmail.com>