SPM: EHF: Build EHF module along with Secure Partition Manager

Add a dependency for building EL3 exception handling framework(EHF)
module with the secure partition manager(SPM).

The EHF module is needed for raising the core's running priority
before the core enters the secure partition, and lowering it
subsequently on exit from the secure partition.

Change-Id: Icbe2d0a63f00b46dc593ff3d86b676c9333506c3
Signed-off-by: Sughosh Ganu <sughosh.ganu@arm.com>

bl31/bl31.mk

@@ -8,6 +8,9 @@
 # Include SPM Makefile
 ################################################################################
 ifeq (${ENABLE_SPM},1)
+ifeq (${EL3_EXCEPTION_HANDLING},0)
+  $(error EL3_EXCEPTION_HANDLING must be 1 for SPM support)
+endif
 $(info Including SPM makefile)
 include services/std_svc/spm/spm.mk
 endif

docs/secure-partition-manager-design.rst

@@ -125,8 +125,9 @@ Interface). This will be referred to as the *Standalone MM Secure Partition* in
 the rest of this document.
 
 To enable SPM support in TF-A, the source code must be compiled with the build
-flag ``ENABLE_SPM=1``. On Arm platforms the build option ``ARM_BL31_IN_DRAM``
-must be set to 1. Also, the location of the binary that contains the BL32 image
+flag ``ENABLE_SPM=1``, along with ``EL3_EXCEPTION_HANDLING=1``. On Arm
+platforms the build option ``ARM_BL31_IN_DRAM`` must be set to 1. Also, the
+location of the binary that contains the BL32 image
 (``BL32=path/to/image.bin``) must be specified.
 
 First, build the Standalone MM Secure Partition. To build it, refer to the