pinctrl: renesas: Factor out common R-Mobile bias handling

The pin control sub-drivers for SH/R-Mobile SoCs contain almost
identical bias handling.  The only SoC-specific part is the mapping from
pin numbers to PORTnCR registers.

Reduce code duplication by factoring out the bias handling to the common
pinctrl.c code.  Use a callback to handle the pin/register mapping.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/20210303132619.3938128-4-geert+renesas@glider.be