pinctrl: add explicit gpio_disable_free pinmux_op

Some pinctrl drivers (Tegra at least) program a pin to be a GPIO in a
completely different manner than they select which function to mux out of
that pin. In order to support a single "free" pinmux_op, the driver would
need to maintain a per-pin state of requested-for-gpio vs. requested-for-
function. However, that's a lot of work when the core already has explicit
separate paths for gpio request/free and function request/free.

So, add a gpio_disable_free op to struct pinmux_ops, and make pin_free()
call it when appropriate.

When doing this, I noticed that when calling pin_request():

    !!gpio == (gpio_range != NULL)

... and so I collapsed those two parameters in both pin_request(), and
when adding writing the new code in pin_free().

Also, for pin_free():

    !!free_func == (gpio_range != NULL)

However, I didn't want pin_free() to know about the GPIO function naming
special case, so instead, I reworked pin_free() to always return the pin's
previously requested function, and now pinmux_free_gpio() calls
kfree(function). This is much more balanced with the allocation having
been performed in pinmux_request_gpio().

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

include/linux/pinctrl/pinmux.h

@@ -73,6 +73,9 @@ struct pinmux_ops {
 	int (*gpio_request_enable) (struct pinctrl_dev *pctldev,
 				    struct pinctrl_gpio_range *range,
 				    unsigned offset);
+	void (*gpio_disable_free) (struct pinctrl_dev *pctldev,
+				   struct pinctrl_gpio_range *range,
+				   unsigned offset);
 };
 
 /* External interface to pinmux */