arm: mvebu: Enable USB EHCI support on Armada XP

This patch enables the USB EHCI support for the Marvell Armada XP (AXP)
SoCs. In compatism to the Armada 38x (A38x), the AXP needs to configure
the USB PLL and the USB PHY's specifically in U-Boot. The A38x has done
this already in the bin_hdr (SPL U-Boot). Without this, accessing the
controller registers in U-Boot or Linux will hang the CPU.

Additionally, the AXP uses a different USB EHCI base address. This
patch also takes care of this by runtime SoC detection in the Marvell
EHCI driver.

Signed-off-by: Stefan Roese <sr@denx.de>
Signed-off-by: Anton Schubert <anton.schubert@gmx.de>
Cc: Marek Vasut <marex@denx.de>
Cc: Luka Perkov <luka.perkov@sartura.hr>