pinctrl: sh-pfc: checker: Add ioctrl register checks

Add checks for generic control register descriptors:
  1. Register addresses must be unique.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/20200110131927.1029-12-geert+renesas@glider.be