Support for generic input output for MX1 family.
The implementation prevents allocation of one pin
by two users, but does not store pointer to the user
description permanently, because this solution
would have bigger memory overhead.

The simple way to integrate code with per BSP
pins setup and allocation is required else all GPIO
registration checking is useless. The function
imx_gpio_setup_multiple_pins() can be used for this
purpose in future.

Signed-off-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>