UPSTREAM: pinmux: sifive: Convert SiFive pinmux to be devicetree based

Add a simple pinctrl node for the IOF registers under the GPIO
controller node to be used by the pinmux driver.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
(cherry picked from commit f6b7dd09ec1d0e122abffad1171d6e0bc4628374)

TEST=none
BUG=none

Change-Id: Ia742ff48d057f64a3ab3cc9a7d63628533bd61b4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/2876313
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
Reviewed-by: Denis Brockus <dbrockus@chromium.org>
Tested-by: Denis Brockus <dbrockus@chromium.org>
Commit-Queue: Denis Brockus <dbrockus@chromium.org>
7 files changed