staging: mt7621-dts: make use of 'reset-gpios' property for pci

staging: mt7621-dts: make use of 'reset-gpios' property for pci

Properly set pins for group pcie as 'gpio' function and declare
gpio's in the pci node to make reset stuff properly functional.
Delete no more needed general reset and previous pers gpio which
is now being used in 'reset-gpios' property.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20200313200913.24321-4-sergio.paracuellos@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>