pinctrl/nomadik: support other alternate-C functions

Upgrade nomadik pinctrl driver to enable selection of other
alternate-C[1-4] functions on some specific ux500 SoC pins.
Handling of those functions is done thanks to PRCM GPIOCR
registers. This was previously managed in PRCMU driver and
it was not really convenient. Idea is to provide a common
way to control all alternate functions.

Note that this improvement does not support the old-fashioned way
used to control nomadik pins, namely the "nmk_config_pin()" function
and its derivatives.

Signed-off-by: Jean-Nicolas Graux <jean-nicolas.graux@stericsson.com>
Reviewed-by: Philippe Langlais <philippe.langlais@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>