Unified - adapt the generation of bignum assembler to use GENERATE

Unified - adapt the generation of bignum assembler to use GENERATE

This gets rid of the BEGINRAW..ENDRAW sections in crypto/bn/build.info.

This also moves the assembler generating perl scripts to take the
output file name as last command line argument, where necessary.

Reviewed-by: Rich Salz <rsalz@openssl.org>