This patch adds support for the Etimer and Ctimer libraries. To support
the Etimer library, we should poll the etimer process every time the
system clock is updated. To do this more efficiently, by taking advantage
of etimer_next_expiration_time() API, we poll the etimer process only
when an 'Event Timer' has expired.
We don't need any platform specific support in order to enable the Ctimer
library since it relies completely on Etimer.
The others timer libraries (Timer and Stime) don't required any specific
platform support as well since they rely on the system Clock module only.
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