pinctrl: sh-pfc: Validate pin tables at runtime

Extend the run-time debug code with checks to ensure there are no
conflicting pin names, numbers, or enumeration values.

This helps catching bugs early.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>