pinctrl: renesas: rcar: Phase out old SH_PFC_PIN_CFG_IO_VOLTAGE flag

Commit 537db25c ("pinctrl: renesas: Add I/O voltage level
flag") introduced new flags to support pins that can switch their
voltage levels between either 1.8V and 3.3V, or between 2.5V and 3.3V.
The old SH_PFC_PIN_CFG_IO_VOLTAGE flag was retained to avoid having to
change existing drivers.

Replace SH_PFC_PIN_CFG_IO_VOLTAGE by SH_PFC_PIN_CFG_IO_VOLTAGE_18_33, to
make the voltage configuration explicit, and to prepare for the advent
of support for more voltage levels.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/ae5f879c093f3e3cd50ba1495975bccfad81237b.1678271030.git.geert+renesas@glider.be