clocksource: Add NPS400 timers driver

Add internal tick generator which is shared by all cores.
Each cluster of cores view it through dedicated address.
This is used for SMP system where all CPUs synced by same
clock source.

Signed-off-by: Noam Camus <noamc@ezchip.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Acked-by: Vineet Gupta <vgupta@synopsys.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>