pinctrl: renesas: Add support for 1.8V/2.5V I/O voltage levels

pinctrl: renesas: Add support for 1.8V/2.5V I/O voltage levels

Currently, the Renesas pin control driver supports pins that can switch
their I/O voltage levels between either 1.8V and 3.3V, or between 2.5V
and 3.3V.  However, some SoCs have pins that can switch between 1.8V and
2.5V.

Add support for this by replacing the separate SH_PFC_PIN_CFG_IO_VOLTAGE
capability and voltage level flags by a 2-bit field, to cover three
possible I/O voltage switching options.

Ported from Linux kernel commit by Geert Uytterhoeven:
b88e733ac517 ("pinctrl: renesas: Add support for 1.8V/2.5V I/O voltage levels")

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>