Split MMIO accessors into pinctrl-imx-mmio.c and build this
file only if Kconfig symbol PINCTRL_IMX_MMIO is selected.
Select PINCTRL_IMX_MMIO Kconfig symbol for all but pinctrl-imx8.c
driver, which does not use the MMIO accessors. This reduces the
amount of code compiled on platforms which do not use the code.
No functional change.
Signed-off-by: Marek Vasut <marex@denx.de>
