reiserfs: don't compile procfs.o at all if no support

* small define cleanup in header
* fix #ifdeffery in procfs.c via Kconfig

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>