[MIPS] MT: Fix setting of XTC.

XTC can only be set if VPA is clear, which it may not be. There is
also the possibility of a back to back c0 register access hazard to
take care of.
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/kernel/vpe.c

@@ -768,10 +768,16 @@ int vpe_run(struct vpe * v)
 	 */
  	write_tc_c0_tcbind((read_tc_c0_tcbind() & ~TCBIND_CURVPE) | v->minor);
 
+	write_vpe_c0_vpeconf0(read_vpe_c0_vpeconf0() & ~(VPECONF0_VPA));
+
+	back_to_back_c0_hazard();
+
         /* Set up the XTC bit in vpeconf0 to point at our tc */
         write_vpe_c0_vpeconf0( (read_vpe_c0_vpeconf0() & ~(VPECONF0_XTC))
                                | (t->index << VPECONF0_XTC_SHIFT));
 
+	back_to_back_c0_hazard();
+
         /* enable this VPE */
         write_vpe_c0_vpeconf0(read_vpe_c0_vpeconf0() | VPECONF0_VPA);