timer: micro/nano abstraction for announcing tick

The gain is two-fold:

- Removes the need of preprocessor conditionals in the timer drivers'
  ISRs.
- Allows removing the duplication of the 'tick announce' code across
  all timer drivers.

Change-Id: I6078a0b00a833c1d1ca76474987c3214a0c05f7b
Signed-off-by: Benjamin Walsh <benjamin.walsh@windriver.com>
2 files changed