Add PADLOCK_ASM to dso_defines rather than lib_defines

Since the padlock code is an engine, the assembler is for a module,
not a library link to when building a program...  there's a
distinction.

Fixes #2311

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8220)