ARM: 6107/1: plat-nomadik: use the MTU clocksrc for sched_clock

This provides some serious scheduling for the Nomadik family by
introducing a sched_clock() using the MTU clock source in the
same manner as e.g. OMAP or U300. This type of solutions has been
discussed at no end in the past, however we need this resolution
for making measurements and using HRTimers.

Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>