scripts: use pkg-config to locate libcrypto

commit 2cea4a7a1885bd0c765089afc14f7ff0eb77864e upstream.

Otherwise build fails if the headers are not in the default location. While at
it also ask pkg-config for the libs, with fallback to the existing value.

Signed-off-by: Rolf Eike Beer <eb@emlix.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>