fix(el3-runtime): set unset pstate bits to default

During a transition to a higher EL some of the PSTATE bits are not set
by hardware, this means that their state may be leaked from lower ELs.
This patch sets those bits to a default value upon entry to EL3.

This patch was tested using a debugger to check the PSTATE values
are correctly set. As well as adding a test in the next patch to
ensure the PSTATE in lower ELs is still maintained after this change.

Change-Id: Ie546acbca7b9aa3c86bd68185edded91b2a64ae5
Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>
diff --git a/make_helpers/defaults.mk b/make_helpers/defaults.mk
index 551b689..b39dcf4 100644
--- a/make_helpers/defaults.mk
+++ b/make_helpers/defaults.mk
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2016-2021, Arm Limited. All rights reserved.
+# Copyright (c) 2016-2022, Arm Limited. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -145,6 +145,9 @@
 # Flag to enable access to the CNTPOFF_EL2 register
 ENABLE_FEAT_ECV			:= 0
 
+# Flag to enable use of the DIT feature.
+ENABLE_FEAT_DIT			:= 0
+
 # By default BL31 encryption disabled
 ENCRYPT_BL31			:= 0