altos: product defines are always in ao_product.h

When all products were built in a single directory, each one had a
separate version of ao_product.h. Now that they all reside in
sub-directories, each directory has its own ao_product.h

This change is needed so that other modules in the system can use the
product defines; otherwise, ao_product.h was not built at the right time.

Signed-off-by: Keith Packard <keithp@keithp.com>