KEYS: Generalise system_verify_data() to provide access to internal content

Generalise system_verify_data() to provide access to internal content
through a callback.  This allows all the PKCS#7 stuff to be hidden inside
this function and removed from the PE file parser and the PKCS#7 test key.

If external content is not required, NULL should be passed as data to the
function.  If the callback is not required, that can be set to NULL.

The function is now called verify_pkcs7_signature() to contrast with
verify_pefile_signature() and the definitions of both have been moved into
linux/verification.h along with the key_being_used_for enum.

Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
index 91a7e04..f7d2ef9 100644
--- a/crypto/asymmetric_keys/Kconfig
+++ b/crypto/asymmetric_keys/Kconfig
@@ -40,8 +40,7 @@
 
 config PKCS7_TEST_KEY
 	tristate "PKCS#7 testing key type"
-	depends on PKCS7_MESSAGE_PARSER
-	select SYSTEM_TRUSTED_KEYRING
+	depends on SYSTEM_DATA_VERIFICATION
 	help
 	  This option provides a type of key that can be loaded up from a
 	  PKCS#7 message - provided the message is signed by a trusted key.  If
@@ -54,6 +53,7 @@
 config SIGNED_PE_FILE_VERIFICATION
 	bool "Support for PE file signature verification"
 	depends on PKCS7_MESSAGE_PARSER=y
+	depends on SYSTEM_DATA_VERIFICATION
 	select ASN1
 	select OID_REGISTRY
 	help