powerpc/64s/idle: avoid POWER9 DD1 and DD2.0 ERAT workaround on DD2.1

DD2.1 does not have to flush the ERAT after a state-loss idle.

Performance testing was done on a DD2.1 using only the stop0 idle state
(the shallowest state which supports state loss), using context_switch
selftest configured to ping-poing between two threads on the same core
and two different cores.

Performance improvement for same core is 7.0%, different cores is 14.8%.
Reviewed-by: NVaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: NNicholas Piggin <npiggin@gmail.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/idle_book3s.S

@@ -542,7 +542,9 @@ pnv_restore_hyp_resource_arch300:
 	 * then clear bit 60 in MMCRA to ensure the PMU starts running.
 	 */
 	blt	cr3,1f
+BEGIN_FTR_SECTION
 	PPC_INVALIDATE_ERAT
+END_FTR_SECTION_IFSET(CPU_FTR_POWER9_DD1 | CPU_FTR_POWER9_DD20)
 	ld	r1,PACAR1(r13)
 	mfspr	r4,SPRN_MMCRA
 	ori	r4,r4,(1 << (63-60))