arm64: mvebu_db-88f3720_defconfig: Enable PINCTRL and GPIO support

This patch enable the PINCTRL and GPIO support, including the GPIO
command on the Armada 3720 DB.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Konstantin Porotchkin <kostap@marvell.com>
Cc: Nadav Haklai <nadavh@marvell.com>