[kernel][formatting] Formatting pass on core kernel code

Also ran through 'astyle -j -A2' prior to running through clang-fmt,
which adds braces to one line conditionals.

Tested: build and runtests on arm and x86

Change-Id: I888c1ce43dbe12a936a3f13d89c5f8dc16ccab6a

[kernel] Lockdep instrument the vm and thread_lock.

- Instrument the locks used by the vm.
- Instrument the thread lock and remainning core kernel code.
- Leaving remaining arch/lib/driver code for a later CL.

Bug: ZX-23
Test: k ut all and system/test/* pass + manual testing.

Change-Id: Ie3f6a27e81bcd1890d63f2fafda3ee233f7969ef

[kernel] Cleanly shutdown DPC thread before shutting down CPU

This change fixes a race condition where a DPC might begin executing,
but not complete before it's CPU has been shutdown. This led to a
relatively rare hang on shutdown (ZX-2273).

We now allow the DPC thread to finish any started DPC before it is
shutdown.

Tested: Booted and shutdown an x64 qemu instance 500,000 times.

ZX-2273 #done

ZX-2228 #comment prereq

Change-Id: I7edc7eee468cd5daa2c86ab7e7c79e6bb474ece7

[kernel][formatting] switch all of core kernel to using c++ comments

Except some doxygen stuff that looks worse in c+ mode.

Change-Id: I82ae6fec0909dbfceb2615190326d55bca721f12

[kernel][dpc] Move dpc code from kernel/lib/ to kernel/kernel/

Ran clang-format on the dpc files as well

Change-Id: Id333fa05b63f1758dd505cb3fd7b6d397d3b247c