rtc: Add support of rtc-mv for MVEBU SoCs

The Armada 370 and Armada XP Socs have the same controller that the
one used in the orion platforms. This patch enables the selection of
rtc-mv with mvebu platforms.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Florian Fainelli <florian@openwrt.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>