pinctrl: sh-pfc: r8a7795: Add bias pinconf support

Implements pull-up and pull-down. On this SoC there is no simple mapping of
GP pins to bias register bits, so we need a table.

Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>