arm: initial support for Marvell Dove SoCs ...

This commit adds minimal support for the Marvell Dove SoC (88AP510) as
first SoC of the Marvell Orion family. Orion SoCs have a different timer,
therefore current mach-mvebu and Armada 370/XP Kconfig and Makefiles are
slightly modified and a new clocksource drivers is added.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>