vc4: Introduce XML-based packet header generation like Intel's.

vc4: Introduce XML-based packet header generation like Intel's.

I really liked this idea, as it should help with management of packet
parsing tools like the CL dump.  The python script is forked off of theirs
because our packets are byte-based instead of dwords, and the changes to
do so while avoiding performance regressions due to unaligned accesses
were quite invasive.

v2: Fix Android.mk paths, drop shebang for python script, fix overlap
    detection.

Acked-by: Jason Ekstrand <jason@jlekstrand.net>
Acked-by: Kenneth Graunke <kenneth@whitecape.org>
Tested-by: Rob Herring <robh@kernel.org>