pinctrl/nomadik: implement pin multiplexing

Implements basic pinmux for the Nomadik pin controller.

The plan is to split the existing singular pin config interface
nmk_config_pin(), nmk_config_pins(), that will configure muxing
and other settings at the same time, into two interfaces
by splitting the code in pinmux and pinctrl and eventually
deleting the old interface and its helper functions when all
users are gone.

nmk_gpio_set_mode() and nmk_gpio_get_mode() are two older
interfaces for just configuring muxing/altfunctions that
will also be replaced in the end.

We take some extra care to handle the glitch-avoidance here,
but it is simpler now since there is only one altsetting per
pingroup so we know immediately if we need to avoid altfunc
C glitches for a certain group.

As part of the makeover implement the .request() and .free()
calls on the GPIO chips and have them call back into the
pinctrl layer to reserve GPIOs.

ChangeLog v1->v2:
- Rebased on pinctrl-mergebase-20120418 so we get the latest
  driver infrastructure where function count is done by a fixed
  value and we can drop a few range checks since this is now
  handled by the core.
- Include a GPIO muxing hunk erroneously part of the pin config
  patch.

Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>