usb: xhci: Add Marvell MVEBU xHCI support

This patch adds DM based support for the xHCI USB 3.0 controller
integrated in the Armada 3700 SoC. It may be extended to be used
by other MVEBU SoCs as well.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Nadav Haklai <nadavh@marvell.com>
Cc: Kostya Porotchkin <kostap@marvell.com>
Cc: Wilson Ding <dingwei@marvell.com>
Cc: Victor Gu <xigu@marvell.com>
Cc: Hua Jing <jinghua@marvell.com>
Cc: Terry Zhou <bjzhou@marvell.com>
Cc: Hanna Hawa <hannah@marvell.com>
Cc: Haim Boot <hayim@marvell.com>
Acked-by: Marek Vasut <marex@denx.de>