pinctrl: sh-pfc: r8a7778: Use lookup function for bias data

Change the data structure and use the generic sh_pfc_pin_to_bias_info()
function to get the register offset and bit information.

Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>