pinctrl: renesas: checker: Check bias pin conflicts

Check that there is only a single entry for each pin with pull-up and/or
pull-down capabilities.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/dbda76f342258f8029f0420fbe3f341a9abd6f01.1640270559.git.geert+renesas@glider.be