pinctrl: renesas: r8a7796: Add missing bias for PRESET# pin

R-Car Gen3 Hardware Manual Errata for Rev. 0.52 of Nov 30, 2016, added
the configuration bit for bias pull-down control for the PRESET# pin on
R-Car M3-W.  Add driver support for controlling pull-down on this pin.

Fixes: 2d40bd24 ("pinctrl: sh-pfc: r8a7796: Add bias pinconf support")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/c479de5b3f235c2f7d5faea9e7e08e6fccb135df.1619785375.git.geert+renesas@glider.be