submodules: add arm-trusted-firmware third-party repository

Change-Id: I080c0a5954d3e4b2d6debdf2a77f32df7329841c
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Reviewed-on: http://review.coreboot.org/10565
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marc.jones@se-eng.com>
diff --git a/.gitmodules b/.gitmodules
index 7d40675..5990f2d 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -9,3 +9,6 @@
 [submodule "vboot"]
 	path = 3rdparty/vboot
 	url = ../vboot.git
+[submodule "arm-trusted-firmware"]
+	path = 3rdparty/arm-trusted-firmware
+	url = ../arm-trusted-firmware.git
diff --git a/3rdparty/arm-trusted-firmware b/3rdparty/arm-trusted-firmware
new file mode 160000
index 0000000..c163ec4
--- /dev/null
+++ b/3rdparty/arm-trusted-firmware
@@ -0,0 +1 @@
+Subproject commit c163ec455b9f7432a8f677b8d35981e6d11b39cb