evm: load an x509 certificate from the kernel

This patch defines a configuration option and the evm_load_x509() hook
to load an X509 certificate onto the EVM trusted kernel keyring.

Changes in v4:
* Patch description updated

Changes in v3:
* Removed EVM_X509_PATH definition. CONFIG_EVM_X509_PATH is used
  directly.

Changes in v2:
* default key patch changed to /etc/keys

Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
diff --git a/security/integrity/iint.c b/security/integrity/iint.c
index 3d2f5b4..2de9c82 100644
--- a/security/integrity/iint.c
+++ b/security/integrity/iint.c
@@ -254,4 +254,5 @@
 void __init integrity_load_keys(void)
 {
 	ima_load_x509();
+	evm_load_x509();
 }