Disable secure self-hosted debug via MDCR_EL3/SDCR

Trusted Firmware currently has no support for secure self-hosted
debug.  To avoid unexpected exceptions, disable software debug
exceptions, other than software breakpoint instruction exceptions,
from all exception levels in secure state.  This applies to both
AArch32 and AArch64 EL3 initialization.

Change-Id: Id097e54a6bbcd0ca6a2be930df5d860d8d09e777
Signed-off-by: dp-arm <dimitris.papastamos@arm.com>
diff --git a/include/common/aarch32/el3_common_macros.S b/include/common/aarch32/el3_common_macros.S
index 463a080..f6b7527 100644
--- a/include/common/aarch32/el3_common_macros.S
+++ b/include/common/aarch32/el3_common_macros.S
@@ -98,6 +98,11 @@
 	orr	r0, r0, #FPEXC_EN_BIT
 	vmsr	FPEXC, r0
 	isb
+
+	/* Disable secure self-hosted invasive debug. */
+	ldr	r0, =SDCR_DEF_VAL
+	stcopr	r0, SDCR
+
 	.endm
 
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