clocksource: time-armada-370-xp: Divorce from local timer API

Separate the armada 370xp local timers from the local timer API.
This will allow us to remove ARM local timer support in the near
future and makes this driver multi-architecture friendly.

Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Tested-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>