ARM: mx51: Remove imx51_add_gpio_keys

There is no need for using a MX51-specific version of imx_add_gpio_keys.

Remove imx51_add_gpio_keys and use imx_add_gpio_keys instead.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
LAKML-Reference: 1302105926-20574-1-git-send-email-fabio.estevam@freescale.com
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>