arch/tile: clarify flush_buffer()/finv_buffer() function names

They are only applicable for locally-homecached memory ranges, so
change their names to {flush,finv}_buffer_local().  Change inv_buffer()
to just do an mf instead of any kind of fancier barrier, since you're
obviously not going to be waiting for anything once the local homecache
is invalidated.

Fix tilepro.c network driver not to bother calling finv_buffer when
stopping the EPP, but just mf after memset to ensure that it will not
see any packet data after we finish stopping; use finv_buffer_remote()
when doing exit-time cleanup.

This also fixes a (not very interesting) generic Linux build failure
where drivers/scsi/st.c declares its own flush_buffer().

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>