staging: mt7621-pci: bindings: update doc accordly to last changes

Properly update bindings documentation with added 'reset-gpios'
property. Delete also 'perst-gpio' which is not being used anymore.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20200313200913.24321-5-sergio.paracuellos@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>