src: add new target for regenerating protocol structs files

src: add new target for regenerating protocol structs files

Introduce a new ninja target

   ninja -C build regen-{PROTO}

eg

   ninja -C build regen-admin_protocol

that will re-create the reference output file based on what the
current pdwtags command emits. A small change is made to squash
whitespace on enum declarations so that introducing a new longer
enum name doesn't trigger re-indent of all existing enum names.

Reviewed-by: Martin Kletzander <mkletzan@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>