ARM: dts: imx6sx-sdb: Fix enet phy regulator

ARM: dts: imx6sx-sdb: Fix enet phy regulator

Bindings for "fixed-regulator" only explicitly support "gpio" property,
not "gpios". Fix by correcting the property name.

The enet PHYs on imx6sx-sdb needs to be explicitly reset after a power
cycle, this can be handled by the phy-reset-gpios property. Sadly this
is not handled on suspend: the fec driver turns phy-supply off but
doesn't assert phy-reset-gpios again on resume.

Since additional phy-level work is required to support powering off the
phy in suspend fix the problem by just marking the regulator as
"boot-on" "always-on" so that it's never turned off. This behavior is
equivalent to older releases.

Keep the phy-reset-gpios property on fec anyway because it is a correct
description of board design.

This issue was exposed by commit 3bfbc244c15a ("regulator: fixed:
Convert to use GPIO descriptor only") which causes the "gpios" property
to also be parsed. Before that commit the "gpios" property had no
effect, PHY reset was only handled in the the bootloader.

This fixes linux-next boot failures previously reported here:
 https://lore.kernel.org/patchwork/patch/982437/#1177900
 https://lore.kernel.org/patchwork/patch/994091/#1178304

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>