pinctrl-tz1090-pdc: add TZ1090 PDC pinctrl driver

Add a pin control driver for the TZ1090's low power pins via the
powerdown controller SOC_GPIO_CONTROL registers.

These pins have individually controlled pull-up, and group controlled
schmitt, slew-rate, drive-strength, and power-on-start (pos).

The pdc_gpio0 and pdc_gpio1 pins can also be muxed onto the
ir_mod_stable_out and ir_mod_power_out functions respectively. If no
function is set they remain in GPIO mode. These muxes can be overridden
by requesting them as GPIOs.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Rob Landley <rob@landley.net>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-doc@vger.kernel.org
Cc: devicetree-discuss@lists.ozlabs.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>