KEYS: trusted: Expose common functionality [ver #2]

This patch exposes some common functionality needed to send TPM commands.
Several functions from keys/trusted.c are exposed for use by the new tpm
key subtype and a module dependency is introduced.

In the future, common functionality between the trusted key type and the
asym_tpm subtype should be factored out into a common utility library.

Signed-off-by: Denis Kenzior <denkenz@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Marcel Holtmann <marcel@holtmann.org>
Reviewed-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: James Morris <james.morris@microsoft.com>
diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
index 88353a9..be70ca6 100644
--- a/crypto/asymmetric_keys/Kconfig
+++ b/crypto/asymmetric_keys/Kconfig
@@ -24,6 +24,7 @@
 config ASYMMETRIC_TPM_KEY_SUBTYPE
 	tristate "Asymmetric TPM backed private key subtype"
 	depends on TCG_TPM
+	depends on TRUSTED_KEYS
 	select CRYPTO_HMAC
 	select CRYPTO_SHA1
 	select CRYPTO_HASH_INFO