pinctrl: renesas: r8a77990: Add drive-strength

According to R-Car Gen3 HW documentation 2.20 onwards, drive-strength is
introduced to r8a77990. It is also documented for r8a774c0. Add it to
the pinctrl driver.

Signed-off-by: LUU HOAI <hoai.luu.ub@renesas.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20220320092542.2308-3-wsa+renesas@sang-engineering.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>