evm: Store and detect metadata inode attributes changes

On stacked filesystem the metadata inode may be different than the one
file data inode and therefore changes to it need to be detected
independently. Therefore, store the i_version, device number, and inode
number associated with the file metadata inode.

Implement a function to detect changes to the inode and if a change is
detected reset the evm_status. This function will be called by IMA when
IMA detects that the metadata inode is different from the file's inode.

Co-developed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>