[POWERPC] Add 1TB workaround for PA6T

PA6T has a bug where the slbie instruction does not honor the large
segment bit.  As a result, we have to always use slbia when switching
context.

We don't have to worry about changing the slbie's during fault processing,
since they should never be replacing one VSID with another using the
same ESID.  I.e. there's no risk for inserting duplicate entries due to a
failed slbie of the old entry.  So as long as we clear it out on context
switch we should be fine.

Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/entry_64.S

@@ -408,6 +408,12 @@ END_FTR_SECTION_IFSET(CPU_FTR_1T_SEGMENT)
 	std	r7,SLBSHADOW_STACKVSID(r9)  /* Save VSID */
 	std	r0,SLBSHADOW_STACKESID(r9)  /* Save ESID */
 
+	/* No need to check for CPU_FTR_NO_SLBIE_B here, since when
+	 * we have 1TB segments, the only CPUs known to have the errata
+	 * only support less than 1TB of system memory and we'll never
+	 * actually hit this code path.
+	 */
+
 	slbie	r6
 	slbie	r6		/* Workaround POWER5 < DD2.1 issue */
 	slbmte	r7,r0