Tegra194: introduce support for `SPD=spmd`

This patch introduces the following changes to enable
compilation for `SPD=spmd` command line option.

* compile plat_spmd_manifest.c
* compile libfdt source files

Verified with the `SPD=spmd` command line option for
Tegra194 platforms.
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>
Change-Id: I7f57aa4f1756b19f78d87415bb80794417174bc8

plat/nvidia/tegra/soc/t194/platform_t194.mk

@@ -70,3 +70,13 @@ BL31_SOURCES		+=	lib/extensions/ras/std_err_record.c		\
 				lib/extensions/ras/ras_common.c			\
 				${SOC_DIR}/plat_ras.c
 endif
+
+# SPM dispatcher
+ifeq (${SPD},spmd)
+# include device tree helper library
+include lib/libfdt/libfdt.mk
+# sources to support spmd
+BL31_SOURCES		+=	plat/common/plat_spmd_manifest.c	\
+				common/fdt_wrappers.c			\
+				${LIBFDT_SRCS}
+endif