Update SeaBIOS to latest upstream

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

roms/seabios

diff --git a/roms/seabios b/roms/seabios
index 5c3f5dd..c604f2f 160000
--- a/roms/seabios
+++ b/roms/seabios
@@ -1 +1 @@
-Subproject commit 5c3f5dde217f382b02350973a38f50941904473d
+Subproject commit c604f2f6be0ad729c8e25958c946a8535ca391ee