tile: convert uses of "inv" to "finv"

The "inv" (invalidate) instruction is generally less safe than "finv"
(flush and invalidate), as it will drop dirty data from the cache.
It turns out we have almost no need for "inv" (other than for the
older 32-bit architecture in some limited cases), so convert to
"finv" where possible and delete the extra "inv" infrastructure.

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

arch/tile/kernel/head_64.S

@@ -77,7 +77,7 @@ ENTRY(_start)
 	{
 	  /* After initializing swapper_pgprot, HV_PTE_GLOBAL is set. */
 	  bfextu r7, r1, HV_PTE_INDEX_GLOBAL, HV_PTE_INDEX_GLOBAL
-	  inv r4
+	  finv r4
 	}
 	bnez r7, .Lno_write
 	{