scons,misc: Update default X86 protocol to MESI_Two_Level

MI_Example is a particularly poor protocol as the default for X86.
MESI_Two_Level is a suitable replacement.

The primary reason for this change is so the vanilla X86 build can run
the X86DemoBoard, submitted here:

Change-Id: I46212f795684bd1f2ce285c69ffcad2f148ab328
Maintainer: Bobby Bruce <>
Tested-by: kokoro <>
Reviewed-by: Bobby Bruce <>
9 files changed