ima: Define asymmetric_verify_v3() to verify IMA sigv3 signatures

ima: Define asymmetric_verify_v3() to verify IMA sigv3 signatures

Define asymmetric_verify_v3() to calculate the hash of the struct
ima_file_id, before calling asymmetric_verify() to verify the
signature.

Move and update the existing calc_file_id_hash() function with a
simpler, self contained version.  In addition to the existing hash
data and hash data length arguments, also pass the hash algorithm.

Suggested-by: Stefan Berger <stefanb@linux.ibm.com>
Tested-by: Stefan Berger <stefanb@linux.ibm.com>
Acked-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>