PKCS#7: Use x509_request_asymmetric_key()

pkcs7_request_asymmetric_key() and x509_request_asymmetric_key() do the same
thing, the latter being a copy of the former created by the IMA folks, so drop
the PKCS#7 version as the X.509 location is more general.

Whilst we're at it, rename the arguments of x509_request_asymmetric_key() to
better reflect what the values being passed in are intended to match on an
X.509 cert.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index fc097326..0d164c6 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -98,4 +98,8 @@
 extern int verify_signature(const struct key *key,
 			    const struct public_key_signature *sig);
 
+extern struct key *x509_request_asymmetric_key(struct key *keyring,
+					       const char *issuer,
+					       const char *key_id);
+
 #endif /* _LINUX_PUBLIC_KEY_H */