sched/hrtimer: Some improvements.

[Fix-Point]

Summary

This main changes of this PR include:

1. Removed nxsched_tick_expiration() function: The tick expiration logic has been integrated into nxsched_process_timer() to simplify the scheduler architecture. Previously, nxsched_tick_expiration() was called from platform-specific code when the tickless timer expired, but now this functionality is handled directly within nxsched_process_timer().

2. Simplified hrtimer API:

   • Changed hrtimer_start() to accept the callback function as a parameter instead of storing it during initialization. The hrtimer is designed to replace the wdog timer in future, so it should have the callback function in its API. The evaluation results showed there is no any performance degradation since the CPU pipeline can hide the latency.
   • Simplified type declarations by using typedef for hrtimer_t and hrtimer_node_t
   • Modified timer armed state checking to use the callback function pointer instead of RB-tree parent pointer

3. Updated documentation: All references to nxsched_tick_expiration() in documentation have been updated to nxsched_process_timer(). Additionally, outdated documentation for watchdog timer functions (wd_restart() and wd_restart_next()) has been removed, and high-resolution timer (hrtimer) documentation has been updated to reflect API changes.

Impact

Documentation:

• Documentation has been updated to reflect the new function names and API changes.
• Outdated wdog timer documentation has been removed.

Performance:

• The hrtimer changes aim to improve code clarity without performance degradation.
• The consolidated timer handling may reduce function call overhead in tickless mode.

Testing

Tested on rv-virt:smp, ostest passed

[GUIDINGLI]

LGTM