ARM platforms: Define exception macros

Define number of priority bits, and allocate priority levels for SDEI.

Change-Id: Ib6bb6c5c09397f7caef950c4caed5a737b3d4112
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>
diff --git a/plat/arm/common/arm_common.mk b/plat/arm/common/arm_common.mk
index 44eb43f..a3cd9d8 100644
--- a/plat/arm/common/arm_common.mk
+++ b/plat/arm/common/arm_common.mk
@@ -184,6 +184,10 @@
 				lib/pmf/pmf_smc.c
 endif
 
+ifeq (${EL3_EXCEPTION_HANDLING},1)
+BL31_SOURCES		+=	plat/arm/common/aarch64/arm_ehf.c
+endif
+
 ifneq (${TRUSTED_BOARD_BOOT},0)
 
     # Include common TBB sources