[zx] Move public zx headers to match naming convention

The zx library provides headers intended for general use, so the
include path should be spelled <lib/zx/foo.h> as per
https://fuchsia.googlesource.com/docs/+/master/development/languages/c-cpp/naming.md.
This moves the headers into the proper location and updates includes to
match.

Change-Id: I6fc9b2a491b5f8b0d270c4dfc77fa4be5739071b

[ddk][io-buffer] Rename callsites of io_buffer_init*_with_bti

ZX-1804 #comment Move all zircon callsites to final name

Change-Id: Ie35de5654841e84653582126dc1f976664c0f49d

[dev][gauss][audio] Replace ZX_VMO_OP_LOOKUP usage with io_buffer_t

Change-Id: Ic3cb938e95b41b9dbe4f378f728717e1e4e7dff2

[ddk][platform-device] Add cache policy argument to contig buffer allocation helpers

For now, keep all clients using cached buffers.

Change-Id: Ia1777f1506f8421da7ccb99a39391a4bc7256427

[gauss][audio] Use pdev_alloc_contig_vmo instead of zx_vmo_create_contiguous

Eliminates need for get_root_resource()

Change-Id: I737de959d85cc0c5b4e50fd9b2954746182e7566

[dev][gauss audio] Handle notifications_per_ring correctly

Previously we were hardcoded to 4 notifications per ring. This did not
bode well with the mixer that expected no notifications per ring.

This CL adds proper handling of notifications per ring. The client
configuration is forwarded to the hardware in case
notifications_per_ring > 0.

Test:
$ ./wav_record --channels=8 --frame-rate=48000 test.wav

Recorded file sounds good.

Change-Id: I8a19fd6b26c5c8f70aa9064eca4c99f1b1f64f38

[dev][gauss audio] Get audio driver recording files

Get basic recording working. Still quite fragile. Known issues:

- Only first record in a boot session works. The driver doesn't attempt
to clean up properly at all yet.
- Recorded bytes != bits/sample * framerate * recording_duration. There
are some extra bytes.
- The driver is tested only talking to 1 client. No attempt to talk to
multiple clients yet.
- The driver only support framerate=48000, bits/sample=16, channels=8.
- The driver ignores min_ring_buffer_frames. Currently the VMO size is
hardcoded to 0x8000.
- The driver ignores notifications_per_ring. It currently sends
notifications every 0x2000 of data.

Bug: 68019773
Test: On gauss:
audio -r 48000 -b 16 -c 8 record test.wav 10
Generates recorded file that sounds quite good.

Change-Id: I3a0cfcc287b8001e8a37971c721c5bfe5bdf6a79