pinctrl: renesas: r8a7794: Add bias pinconf support

Implement support for pull-up (most pins) and pull-down (ASEBRK#/ACK)
handling for R-Car E2 and RZ/G1E SoCs, using the common R-Car bias
handling.

Note that on RZ/G1E, the "ASEBRK#/ACK" pin is called "ACK", but the code
doesn't handle that naming difference.  Hence users should use the R-Car
naming in DTS files.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/f78da2ba937ce98ae9196f4ee54149a5214fd545.1619785375.git.geert+renesas@glider.be