[Performance Improvement] Change the rdev->lock in struct rpmsg_device from mutex to spinlock

[CV-Bowen]

I noticed that rdev->lock can be changed to spinlock(with irqsave/irqrestore) to improve the performace, what do you think. @arnopo @edmooring @tnmysh
If so, I can't create a PR to do this.

[tnmysh]

I am not sure what do you mean by spinlock. Could you please give link to code which is refrenced above (rdev->lock) ?

[github-actions]

This issue has been marked as a stale issue because it has been open (more than) 45 days with no activity.