regulator: gpio: Convert to use descriptors

This converts the GPIO regulator driver to use decriptors only.

We have to let go of the array gpio handling: the fetched descriptors
are handled individually anyway, and the array retrieveal function
does not make it possible to retrieve each GPIO descriptor with
unique flags. Instead get them one by one.

We request the "enable" GPIO separately as before, and make sure
that this line is requested as nonexclusive since enable lines can
be shared and the regulator core expects this.

Most users of the GPIO regulator are using device tree.

There are two boards in the kernel using the gpio regulator from a
non-devicetree path: PXA hx4700 and magician. Make sure to switch
these over to use descriptors as well.

Cc: Philipp Zabel <p.zabel@pengutronix.de> # Magician
Cc: Petr Cvek <petr.cvek@tul.cz> # Magician
Cc: Robert Jarzmik <robert.jarzmik@free.fr> # PXA
Cc: Paul Parsons <lost.distance@yahoo.com> # hx4700
Cc: Kevin Hilman <khilman@baylibre.com> # Meson
Cc: Neil Armstrong <narmstrong@baylibre.com> # Meson
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>