Add support for selecting encryption backend

- Add two new module parameters to icp (icp_aes_impl, icp_gcm_impl)
  that control the crypto implementation.  At the moment there is a
  choice between generic and aesni (on platforms that support it).
- This enables support for AES-NI and PCLMULQDQ-NI on AMD Family
  15h (bulldozer) and newer CPUs (zen).
- Modify aes_key_t to track what implementation it was generated
  with as key schedules generated with various implementations
  are not necessarily interchangable.

Reviewed by: Gvozden Neskovic <neskovic@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tom Caputi <tcaputi@datto.com>
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Signed-off-by: Nathaniel R. Lewis <linux.robotdude@gmail.com>
Closes #7102 
Closes #7103

include/sys/crypto/icp.h

@@ -44,4 +44,7 @@ int skein_mod_fini(void);
 int icp_init(void);
 void icp_fini(void);
 
+int aes_impl_set(const char *);
+int gcm_impl_set(const char *);
+
 #endif /* _SYS_CRYPTO_ALGS_H */