arch/x86: Add debug spinloop

Conditionally add a debug spinloop to enable easy connection of JTAG
debuggers.

TEST=Build and run on Galileo Gen2 with a JTAG debugger.

Change-Id: I7a21f9e6bfb10912d06ce48447c61202553630d0
Signed-off-by: Lee Leahy <leroy.p.leahy@intel.com>
Reviewed-on: https://review.coreboot.org/15127
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
2 files changed