target/ppc/spapr_caps: Add new tristate cap safe_cache
    
    Add new tristate cap cap-cfpc to represent the cache flush on privilege
    change capability.
    
    Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
    Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
    Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
    (cherry picked from commit 8f38eaf8f9dd194c9961cf76c675724930ce4570)
    Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>