For ARM currently TIMER_PRECISION exists, but that is in microseconds
and not fine-grained enough.

This is needed to make periodic tasks synchronous with the system clock.
If this value is zero every period will be extended with the overhead of
taking an interrupt and reading the system clock. To avoid this drift,
the configured value should be set to at least the average overhead.

See also issue #844.

Signed-off-by: Indan Zupancic <Indan.Zupancic@mep-info.com>