-gc and -vrq update for v4.2.4

There are API updates in v4.2.4, so here comes the -gc and -vrq branch updates.

You can checkout the latest code from bitbucket or github for gc branch. Main sync-up commit is e8d2e33 bfs: [Sync] sync-up with v4.2.4 

For -vrq branch, besides the sync-up commit 2f4a9ac bfs: [Sync] sync-up with v4.2.4, there is a bug fix commit 7de8ad5 bfs/vrq: Fix preemptible code in sys_sched_yield(), this commit is to address smp_processor_id() in preemptible [00000000] code error in sys_sched_yield(). Vrq branch is updated at bitbucket and github.

BR Alfred