Mark unused pinctrl and wuc nodes in it8xxx2 with /omit-if-no-ref/,
so that they are omitted from the final devicetree when not referenced.
After this change, test: "west build -p always -b it8xxx2_evb" shows a
reduction in devicetree size:
Before:
build/zephyr/zephyr.dts 164,449 bytes
build/zephyr/include/generated/zephyr/devicetree_generated.h
3,125,359 bytes
After:
build/zephyr/zephyr.dts 124,108 bytes
build/zephyr/include/generated/zephyr/devicetree_generated.h
1,892,313 bytes
Signed-off-by: Tim Lin <tim2.lin@ite.corp-partner.google.com>