x86: Add support for building up an NHLT structure

The Intel Non-High-Definition-Audio Link Table (NHLT) table describes the
audio codecs and connections in a system. Various devices can contribute
information to produce the table.

Add functions to allow adding to the structure that is eventually written
to the ACPI tables. Also add the device-tree bindings.

Signed-off-by: Simon Glass <sjg@chromium.org>