evm_inode_init_security and module stacking

[Casey Schaufler]

security_inode_init_security() currently calls at most one
of selinux_inode_init_security() and smack_inode_init_security().
It then sends the result to evm_inode_init_security to create
the security.evm attribute. This isn't going to work on a system
that has both SELinux and Smack.

I see two options:
	- create security.evm with the information from all
	  security modules that provide inode_init_security hooks
	- create a separate attribute for each module,
	  security.evm-selinux and security.evm-smack in the
	  current case.

How would you like to have it work? I am agnostic, although the
separate attributes would be easier for the infrastructure.