arm: mvebu: update defconfig with PCI and USB support

Now that we have the necessary drivers and Device Tree informations to
support PCIe on Armada 370 and Armada XP, enable the CONFIG_PCI
option.

Also, since the Armada 370 Mirabox has a built-in USB XHCI controller
connected on the PCIe bus, enable the corresponding options as well.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>