drivers: pinmux: pinmux_mcux: Convert to devicetree

Use a similar model to the pinmux_rv32m1 driver for kinetis pinmux
driver.  We handle one subtle difference between clock on the KE1xF v
other SoCs.

As the Kconfig and devicetree label names are the same we maintain the
Kconfig options in the driver until all board users are converted over
to use devicetree instead of Kconfig.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>