pinctrl: sh-pfc: r8a7796: Use generic bias register description

Move R-Car M3-W bias support over to the generic way to describe bias
registers, which will be needed for suspend/resume support.

As the new description is more compact, this decreases kernel size by
ca. 304 bytes.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>