Add pinctrl driver for imx8-based platforms

[dreamliner787-9]

This PR adds implmentation and documentations of the pinctrl subsystem and driver for imx8-based platforms.

Limitations:

• Dynamic configuration of pinctrl registers at runtime is unsupported as the client interface are being worked out. Currently, the driver will only set the default configuration.
• "Quirky" select input values on imx8 platforms are unsupported (https://github.com/torvalds/linux/blob/c94d59a126cb9a8d1f71e3e044363d654dcd7af8/drivers/pinctrl/freescale/pinctrl-imx.c#L198C1-L199C1). Though as far as I can tell, these values only exists in some vendor specific kernels and never made it to mainline Linux.

Checklist before we can merge this:

• [ ] Merge https://github.com/au-ts/microkit_sdf_gen/pull/14
• [x] Add pinctrl example to hardware CI