pinctrl: sh-pfc: r8a7795: Support none GPIO pins bias setting

There are pins on the r8a7795 which are not part of a GPIO bank nor
can be muxed between different functions. They do however allow for the
bias to be configured. Add those pins to the list of pins and
to the bias configuration array.

The pins can now be referred to in DT by function names and their bias
setting set.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>