pinctrl: imx: Rename imx_pinctrl_remove() to imx_pinctrl_remove_mmio()

pinctrl: imx: Rename imx_pinctrl_remove() to imx_pinctrl_remove_mmio()

The current implementation of imx_pinctrl_remove() is specific
to the MMIO accessor implementation, rename the function to
imx_pinctrl_remove_mmio() to make this obvious. No functional
change.

Signed-off-by: Marek Vasut <marex@denx.de>