arm64: a37xx: pci: Make PCIe Reset GPIO DT compatible with Linux kernel DT

Change active-high to active-low and change DT property name from
reset-gpio to reset-gpios. This format of gpio reset is used by
pci-aardvark driver in Linux kernel.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Konstantin Porotchkin <kostap@marvell.com>
Tested-by: Andre Heider <a.heider@gmail.com>