ARM: choose highest resolution delay timer

In case there are several possible delay timers, choose the one with the
highest resolution. This code relies on the fact secondary CPUs have not yet
been brought online when register_current_timer_delay() is called. This is
ensured by implementing calibration_delay_done(),

Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Stephen Warren <swarren@nvidia.com>