hexagon: use generic fixmap.h

Signed-off-by: Mark Salter <msalter@redhat.com>
Acked-by: Richard Kuo <rkuo@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>