ARM: 7310/1: integrator: implement sched_clock across all boards

Now that we can select a sched_clock at runtime, let's implement
it for the Integrator AP, default-select the one found in all
other board it for all plat-versatile boards and make the right
clock kick in at runtime.

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