[common] tick a time routine for code profiling

[common] tick a time routine for code profiling

call like this:

  timer_initialise(); // place near start of program
  // ...

  unsigned int t1, t2;

  t1 = tick_get();
  // some code here
  t2 = tick_get();

  // show result (MCLK_MHz from wikireader.h)
  // use appropriate display
  DISPLAY("elapsed time = %u uS\n", (t2 - t1) / MCLK_MHz);

Note:
  Timer will be stopped by suspend, so disable this feature
  when profiling.

Signed-off-by: Christopher Hall <hsw@openmoko.com>
git-svn-id: https://wikipediardware.googlecode.com/svn/trunk@1473 974c56cd-8151-0410-98c4-7bb2f43fa8c1