regulator: fixed: Add support for gpios prop

The commit 12df2c182ccb ("regulator: dt-bindings: fixed-regulator: allow
gpios property") in linux v6.3-rc1 added support for use of either a
gpios or gpio prop with a fixed-regulator.

This adds support for the new gpios prop to the fixed-regulator driver.
gpios prop is used by vcc3v3-pcie-regulator on Radxa ROCK 3 Model A.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>