pinctrl: renesas: checker: Move overlapping field check

Move the check for overlapping drive register fields from
sh_pfc_check_drive_reg() to sh_pfc_check_reg(), so it can be used for
other register types, too.  This requires passing the covered register
bits to sh_pfc_check_reg().

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/9d75057200890bbf31e226ffcc4514ecc5bc2c34.1633615652.git.geert+renesas@glider.be