icsf: update de/encryption functions to return the expected length

Update icsf_secret_key_encrypt() and icsf_secret_key_decrypt() to
returned the expected length of the output buffer when it is NULL.

Signed-off-by: Marcelo Cerri <mhcerri@linux.vnet.ibm.com>
icsf: add token-specific functions to de/encrypt data

Add the token-specific functions related to the following PKCS#11
functions:

 - C_EncryptInit()
 - C_Encrypt()
 - C_EncryptUpdate()
 - C_EncryptFinal()
 - C_DecryptInit()
 - C_Decrypt()
 - C_DecryptUpdate()
 - C_DecryptFinal()