arm: mvebu: update defconfig with local timer support

Now that we have support for local timers, enable it by default

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
arm: mvebu: update DT to support local timers

Now that the time-armada-370-xp support local timers, updated the
device tree to take it into account.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
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>