arm: mvebu/kirkwood: Use common timer functions

By using the common timer functions for mvebu/kirkwood we can get rid of quite
a lot of code.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Luka Perkov <luka.perkov@sartura.hr>
Cc: Simon Guinot <simon.guinot@sequanux.org>
Cc: Valentin Longchamp <valentin.longchamp@keymile.com>