at91_cf: use generic gpio calls

Update the AT91 CF driver to use the generic GPIO calls instead of the
AT91-specific ones; and request exclusive use of those signals.

Minor tweaks to cleanup code paths: always in reverse order of how the
resources were allocated, with remove() matching the fault paths of
probe().

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>