s390x: Hide internal cpuid symbol and function

s390x: Hide internal cpuid symbol and function

The symbol OPENSSL_s390xcap_P and the OPENSSL_cpuid_setup function are not
exported by the version script of OpenSSL.  However, if someone uses the
static library without the version script, these symbols all of a sudden
become global symbols and their usage in assembler code does not correctly
reflect that for PIC.  Since these symbols should never be used outside of
OpenSSL, hide them inside the binary.

Signed-off-by: Juergen Christ <jchrist@linux.ibm.com>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17946)