roms: Add virtual Boot ROM for NPCM7xx SoCs

This is a minimalistic boot ROM written specifically for use with QEMU.
It supports loading the second-stage loader from SPI flash into RAM, SMP
boot, and not much else.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Havard Skinnemoen <hskinnemoen@google.com>
Message-id: 20200911052101.2602693-7-hskinnemoen@google.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/.gitmodules b/.gitmodules
index ce97939..9ffb9f3 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -61,3 +61,6 @@
 [submodule "meson"]
 	path = meson
 	url = https://github.com/mesonbuild/meson/
+[submodule "roms/vbootrom"]
+	path = roms/vbootrom
+	url = https://github.com/google/vbootrom.git