soc: nxp: imx*: remove redundant pinctrl defconfig

Many NXP socs had the following defconfig:

```
config PINCTRL_IMX
	default y if HAS_IMX_IOMUXC
	depends on PINCTRL
```

However, the PINCTRL_IMX option already has:

```
config PINCTRL_IMX
	bool "Pin controller driver for iMX MCUs"
	depends on DT_HAS_NXP_IMX_IOMUXC_ENABLED
	depends on HAS_MCUX_IOMUXC || HAS_IMX_IOMUXC
	default y
	help
	  Enable pin controller driver for NXP iMX series MCUs
```

So the soc level defconfigs are redundant.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>