Streamline the LinuxKPI spinlock wrappers.

1. Add better spinlock debug names when WITNESS_ALL is defined.

2. Make sure that the calling thread gets bound to the current CPU

while a spinlock is locked. Some Linux kernel code depends on that the
CPU ID doesn't change while a spinlock is locked.

3. Add support for using LinuxKPI spinlocks during a panic().

MFC after: 1 week
Sponsored by: Mellanox Technologies