clocksource: update and move armada-370-xp-timer documentation to timer directory

Timer driver for Armada 370 and Armada XP have gained local timers
support. So it needs new resources information regarding the IRQs
and the registers.

Also move the documentation in the new and more accurate directory

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>

Documentation/devicetree/bindings/timer/marvell,armada-370-xp-timer.txt

@@ -0,0 +1,15 @@
+Marvell Armada 370 and Armada XP Timers
+---------------------------------------
+
+Required properties:
+- compatible: Should be "marvell,armada-370-xp-timer"
+- interrupts: Should contain the list of Global Timer interrupts and
+  then local timer interrupts
+- reg: Should contain location and length for timers register. First
+  pair for the Global Timer registers, second pair for the
+  local/private timers.
+- clocks: clock driving the timer hardware
+
+Optional properties:
+- marvell,timer-25Mhz: Tells whether the Global timer supports the 25
+  Mhz fixed mode (available on Armada XP and not on Armada 370)