Set up 3rdparty/libhwbase

`libhwbase` is a SPARK library that contains some basic support for i/o
access, debugging, timers. Just what I put around `libgfxinit`, to make
it build standalone.

Change-Id: I1918680c14696215522e1c5dae072235bb4e71a3
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/16948
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
diff --git a/.gitmodules b/.gitmodules
index ad6b899..c545ccd 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -15,3 +15,6 @@
 [submodule "3rdparty/chromeec"]
 	path = 3rdparty/chromeec
 	url = ../chrome-ec.git
+[submodule "libhwbase"]
+	path = 3rdparty/libhwbase
+	url = ../libhwbase.git