uma: Add KASAN state transitions

• Add a UMA_ZONE_NOKASAN flag to indicate that items from a particular zone should not be sanitized. This is applied implicitly for NOFREE and cache zones.
• Add KASAN call backs which get invoked:
  1. when a slab is imported into a keg
  2. when an item is allocated from a zone
  3. when an item is freed to a zone
  4. when a slab is freed back to the VM
     
     In state transitions 1 and 3, memory is poisoned so that accesses will trigger a panic. In state transitions 2 and 4, memory is marked valid.
• Disable trashing if KASAN is enabled. It just adds extra CPU overhead to catch problems that are detected by KASAN.

MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D29456