Add seabios build scripts to roms/

Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

roms/Makefile

+
+default:
+	@echo "nothing is build by default"
+	@echo "available build targets:"
+	@echo "  bios           -- update bios.bin (seabios)"
+
+bios: config.seabios
+	sh configure-seabios.sh $<
+	make -C seabios out/bios.bin
+	cp seabios/out/bios.bin ../pc-bios/bios.bin

roms/config.seabios

+# empty, default config works for us

roms/configure-seabios.sh

+#!/bin/sh
+config="$1"
+make -C seabios clean distclean
+cp "$config" seabios/.config
+make -C seabios oldnoconfig