Aarch64: Add support for FEAT_PANx extensions

This patch provides the changes listed below:
- Adds new bit fields definitions for SCTLR_EL1/2 registers
- Corrects the name of SCTLR_EL1/2.[20] bit field from
SCTLR_UWXN_BIT to SCTLR_TSCXT_BIT
- Adds FEAT_PANx bit field definitions and their possible
values for ID_AA64MMFR1_EL1 register.
- Adds setting of SCTLR_EL1.SPAN bit to preserve PSTATE.PAN
on taking an exception to EL1 in spm_sp_setup() function
(services\std_svc\spm_mm\spm_mm_setup.c)

Change-Id: If51f20e7995c649126a7728a4d0867041fdade19
Signed-off-by: Alexei Fedorov <Alexei.Fedorov@arm.com>
diff --git a/services/std_svc/spm_mm/spm_mm_setup.c b/services/std_svc/spm_mm/spm_mm_setup.c
index 468e5b3..32562c3 100644
--- a/services/std_svc/spm_mm/spm_mm_setup.c
+++ b/services/std_svc/spm_mm/spm_mm_setup.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2017-2020, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -142,6 +142,8 @@
 		SCTLR_DZE_BIT							|
 		/* Enable SP Alignment check for EL0 */
 		SCTLR_SA0_BIT							|
+		/* Don't change PSTATE.PAN on taking an exception to EL1 */
+		SCTLR_SPAN_BIT							|
 		/* Allow cacheable data and instr. accesses to normal memory. */
 		SCTLR_C_BIT | SCTLR_I_BIT					|
 		/* Enable MMU. */