[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[zircon][mxtl->fbl] Rename mxtl to fbl

Change-Id: Ie21b6498e1bfb0a7fa0315e40b9e5c3ee78646be

[kernel][dev] Remove an unused header inclusion

Change-Id: If538b5e3370a9131fd303720a4970b495f1efeb3

[kernel][atomics] Move private/magenta/atomic.h into the kernel

This is now only used by kernel C code. Everything else is either C++
and is using mxtl::atomic, or is in userspace and can use the standard
C11 versions.

Change-Id: I113d3e1c7fe6a1bbe3d0e54cd6cbac8b62ccd194

[pcie] Fix the release build

Fix the release build by updating the PCI device refcount re-direct
hack. mxtl::RefPtr now always calls Adopt, but it expects Adopt to be
an inline no-op in a release build.

Change-Id: I3b8e7f78c9eae8da71dfcce1fe1e01c79282aaf1

[assert] Introduce MX_ASSERT

Make magenta style asserts public and defined in magenta/assert.h. Convert
usermode code to use the MX_(ASSERT|DEBUG_ASSERT) versions.

Change-Id: Iec8cc20f9c577cee50bc72bd820d4c1b604b8a86

[pcie] Change how ref-counting works.

Eliminate the confusing ref-count redirects introduced to deal with
multiple inheritance issues. Instead, leverage vtables and some
macros to implement something which behaves much like virtual
inheritance, but without actually using virtual inheritance. See the
extensive document in pcie_ref_counted.h for details.

Change-Id: I8dd7e400f2a25ca2296d8f50c580f76ab3c3cf39