add sgabios blob and submodule

The rom was not added together with the sgabios device and is
not installed.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/.gitmodules b/.gitmodules
index 2a43dbc..eca876f 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -16,3 +16,6 @@
 [submodule "roms/qemu-palcode"]
 	path = roms/qemu-palcode
 	url = git://repo.or.cz/qemu-palcode.git
+[submodule "roms/sgabios"]
+	path = roms/sgabios
+	url = git://git.qemu.org/sgabios.git