gpio: of: Handle both enable-gpio{,s}

Handle both enable-gpio and enable-gpios properties of the GPIO
regulator in the quirk. The later is the preferred modern name
of the property.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Jan Kotas <jank@cadence.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Thierry Reding <treding@nvidia.com>
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: linux-renesas-soc@vger.kernel.org
To: linux-gpio@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>