Add support for configuring all gpio pin modes

[antoinevg]

Adds a new function to firmware gpio drivers to make it possible to enable setting of pin modes for a given GPIO:

/**
 * Configures the system's pinmux to route the given GPIO pin to a physical pin
 * and apply the given pin configuration.
 */
int gpio_configure_pinmux_and_pin(gpio_pin_t pin, gpio_pin_configuration_t pin_configuration);

I did consider removing the - IMO now redundant -- gpio_configure_pinmux_and_resistors() infrastructure but there may be someone out there making use of it?

[martinling]

This looks good to me.

Regarding gpio_configure_pinmux_and_resistors: I agree it would be cleaner to remove this. It appears in the platform_gpio.h API, but that's only public in the very limited context of someone writing their own libgreat platform.

I only found one public project that does so: https://github.com/bm16ton/greatfet-lpc4370, and they did so by just forking the whole GreatFET project.

So I think it could probably be done safely, but I also don't see a need to do that in this PR.

So I think this is good to go.