intel/genxml: Assert that genxml field start and ends are sane.

intel/genxml: Assert that genxml field start and ends are sane.

Chris recently fixed a bunch of genxml end < start bugs, as well as
booleans that are wider than a bit.  These are way too easy to write, so
asserting that the fields are sane is a good plan.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Acked-by: Jason Ekstrand <jason@jlekstrand.net>