pinctrl: sh-pfc: Validate enum IDs for regs with fixed-width fields

Add build-time checks to the PINMUX_CFG_REG() and PINMUX_DATA_REG()
macros, to ensure the number of provided enum IDs is correct.

This helps catching bugs early.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>