iMX51: introduce IMX_GPIO_NR

iMX51: introduce IMX_GPIO_NR

Currently, to define a GPIO number, we're using something like :

#define EFIKAMX_PCBID0         (2*32 + 16)

to define GPIO 3 16.

This is not really readable and it's error prone imho (note the 3 vs 2).
So, I'm introducing a new macro to define this in a better way. Now, the
code sample become :

#define EFIKAMX_PCBID0         IMX_GPIO_NR(3, 16)

v2:
- move to gpio.h
- add parens & spaces
- switch to IMX_GPIO_NR instead of MX51_GPIO_NR

Signed-off-by: Arnaud Patard <arnaud.patard@rtp-net.org>
Cc: Amit Kucheria <amit.kucheria@linaro.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Eric Bénard <eric@eukrea.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>