crypto: tcrypt - add skcipher speed for given alg

Allow to run skcipher speed for given algorithm.
Case 600 is modified to cover ENCRYPT and DECRYPT
directions.

Example:
   modprobe tcrypt mode=600 alg="qat_aes_xts" klen=32

If succeed, the performance numbers will be printed in dmesg:
   testing speed of multibuffer qat_aes_xts (qat_aes_xts) encryption
   test 0 (256 bit key, 16 byte blocks): 1 operation in 14596 cycles (16 bytes)
   ...
   test 6 (256 bit key, 4096 byte blocks): 1 operation in 8053 cycles (4096 bytes)

Signed-off-by: Sergey Portnoy <sergey.portnoy@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>