Add sha384 implementation to sha512_ssse3 module.

This also fixes sha512_ssse3 module autoloading issue when 'sha384' is used
before 'sha512'. Previously in such case, just sha512_generic was loaded and
not sha512_ssse3 (since it did not provide sha384). Now if 'sha512' was used
after 'sha384' usage, sha512_ssse3 would remain unloaded. For example, this
happens with tcrypt testing module since it tests 'sha384' before 'sha512'.

Cc: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>