mvebu: pcie: Add support for GPIO reset for PCIe device

Add support for "marvell,reset-gpio" property to mvebu DW PCIe
driver.
This option is valid when CONFIG_DM_GPIO=y

Change-Id: Ic17c500449050c2fbb700731f1a9ca8b83298986
Signed-off-by: Konstantin Porotchkin <kostap@marvell.com>
Signed-off-by: Rabeeh Khoury <rabeeh@solid-run.com>
Cc: Stefan Roese <sr@denx.de>
Cc: Nadav Haklai <nadavh@marvell.com>
Cc: Neta Zur Hershkovits <neta@marvell.com>
Cc: Igal Liberman <igall@marvell.com>
Cc: Haim Boot <hayim@marvell.com>
Signed-off-by: Stefan Roese <sr@denx.de>