Folds this routine into task_tick_get(), since their co-location
into the same file means that there is no need for one to be a
wrapper function for the other. Also enhances the comments describing
the resulting routine.
Change-Id: I23210991b13be8864af0faf7e1fc4f23aa9252c2
Signed-off-by: Allan Stephens <allan.stephens@windriver.com>