The 25 MHz reference clock has better stability so its use is preferred over the
core clock.

This commit takes advantage of the already introduced Armada 375 devicetree
compatible string and adds a new timer initialization. If available, the timer
will use the reference clock (named as 'fixed'). Otherwise, it falls back to the
previous behavior.
Acked-by: NJason Cooper <jason@lakedaemon.net>
Acked-by: NGregory CLEMENT <gregory.clement@free-electrons.com>
Acked-by: NWim Van Sebroeck <wim@iguana.be>
Reviewed-by: NThomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: NThomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: NEzequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>