ARM: configs: enable XHCI mvebu support in multi_v7_defconfig

The Marvell Armada 38x platform needs the xhci_mvebu driver enabled
for the xHCI USB hosts, so this commit enables the corresponding
Kconfig option in multi_v7_defconfig.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: arm@kernel.org
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Olof Johansson <olof@lixom.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>