uml: export hostfs symbols

Add some exports for hostfs that are required after Alberto Bertogli's fixes
for accessing unlinked host files.

Also did some style cleanups while I was here.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>