pca953x: support GPIOLIB GPIO naming

Add support to the PCA953x driver to use the GPIOLIB naming facility for
GPIOs.

Signed-off-by: Daniel Silverstone <dsilvers@simtec.co.uk>
Cc: Ben Gardner <bgardner@wabtec.com>
Cc: Jean Delvare <khali@linux-fr.org>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>