drivers/gpio/gpio-generic.c: fix build errors

Building a kernel with hotplug disabled results in a link failure:

  `bgpio_remove' referenced in section `___ksymtab_gpl+bgpio_remove' of drivers/built-in.o: defined in discarded section `.devexit.text' of drivers/built-in.o

This is because of bgpio_remove() is exported.  It is illegal to export
symbols which are discarded either at link time or as part of an
init/exit section.

Fix this by dropping the __devexit attributation from bgpio_remove().
Also drop the __devinit attributation from bgpio_init().

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>