cputlb: Add functions for flushing TLB for a single MMU index

cputlb: Add functions for flushing TLB for a single MMU index

Guest CPU TLB maintenance operations may be sufficiently
specialized to only need to flush TLB entries corresponding
to a particular MMU index. Implement cputlb functions for
this, to avoid the inefficiency of flushing TLB entries
which we don't need to.

Signed-off-by: Peter Maydell <[email protected]>
Reviewed-by: Edgar E. Iglesias <[email protected]>
Message-id: 1439548879[email protected]