doc: Document newly added optimizations

* doc/gcrypt.texi: Add HW features 'intel-vaes-vpclmul', 'ppc-vcrypto',
'ppc-arch_3_00', 'ppc-arch_2_07', 's390x-msa', 's390x-msa-4',
's390x-msa-8' and 's390x-vx'.

[jk: fixed "pc-" and "390x-" typos to "ppc-" and "s390x-" ]

• Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
• GnuPG-bug-id: T5337