nxp: imx8ulp: enable pinctrl

This commit enables pinctrl on i.MX8ULP. This includes:
	1) Adding `pinctrl_soc.h` header file.
	2) Adding DTS node for IOMUXC1, which is one of the
	IPs responsible for managing the 8ULP pads.
	3) Adding .dtsi with pin definitions. For now, only
	the LPUART7 pads are added to this file because this
	is going to be the only consummer for now.
	4) Modifying the `pinctrl_imx.c` driver to work for 8ULP.
	5) Enabling the `CONFIG_HAS_MCUX_IOMUXC`, which is a
	dependency of `CONFIG_PINCTRL_IMX`.

Signed-off-by: Laurentiu Mihalcea <laurentiu.mihalcea@nxp.com>