clocksource: Add Marvell Orion SoC timer

This patch add a DT enabled driver for timers found on Marvell Orion SoCs
(Kirkwood, Dove, Orion5x, and Discovery Innovation). It installs a free-
running clocksource on timer0 and a clockevent source on timer1.
Corresponding device tree documentation is also added.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Tested-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Tested-by: Andrew Lunn <andrew@lunn.ch>
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 0a04257..c082e3e 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -25,6 +25,11 @@
 config ARMADA_370_XP_TIMER
 	bool
 
+config ORION_TIMER
+	select CLKSRC_OF
+	select CLKSRC_MMIO
+	bool
+
 config SUN4I_TIMER
 	bool