rom.sh: Add U-Boot before SeaBIOS and GRUB (x86)

Since U-Boot must be inserted at a specific offset, it's
theoretically possible that other files might overlap, but
cbfstool will work around wherever U-Boot was inserted if
it was inserted first; we don't use specific offsets for
the other files.

This is technically a preventative bug fix, but it fixes
a bug that would probably never occur in practise.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/rom.sh

@@ -130,6 +130,11 @@ mkcorebootbin()
 
 add_seabios()
 {
+	if [ "$payload_uboot_i386" = "y" ] || \
+	    [ "$payload_uboot_amd64" = "y" ]; then
+		$dry add_uboot
+	fi
+
 	_seabioself="elf/seabios/default/$initmode/bios.bin.elf"
 
 	cbfs "$tmprom" "$_seabioself" "fallback/payload"
@@ -144,11 +149,6 @@ add_seabios()
 	[ "$payload_memtest" = "y" ] && cbfs "$tmprom" \
 	    "elf/memtest86plus/memtest.bin" img/memtest
 
-	if [ "$payload_uboot_i386" = "y" ] || \
-	    [ "$payload_uboot_amd64" = "y" ]; then
-		$dry add_uboot
-	fi
-
 	[ "$payload_grub" = "y" ] && add_grub
 
 	cprom