Revert "PCI: imx6: Add support for active-low reset GPIO"

Commit 5c5fb40d ("PCI: imx6: Add support for active-low reset GPIO")
cause regressions on some boards like MX6 Gateworks Ventana, for example.

The reason for the breakage is that this commit sets the GPIO polarity in
the wrong logic level.

Also, the commit log is wrong because active-low reset GPIO is what the
driver used to support since the beginning.

So keep the old behavior that ignores the GPIO polarity specified in the
device tree and treat the PCI reset GPIO as active-low.

Reported-by: Krzysztof Hałasa <khalasa@piap.pl>
Tested-by: Tim Harvey <tharvey@gateworks.com>	# Gateworks Ventana
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Tim Harvey <tharvey@gateworks.com>
Acked-by: Lucas Stach <l.stach@pengutronix.de>
CC: stable@vger.kernel.org	# v4.5+