Fix the aes-xts key-length checking condition and hw declaration.

Fix the aes-xts key-length checking condition and hw declaration.

The argument `key-length` includes 2 sets of keys.

All declarations should under `PROV_CIPHER_HW_declare_xts()` macro.

Signed-off-by: Jerry Shih <jerry.shih@sifive.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21923)