x86: configs: add debug_diffconfig This diffconfig is intended to be used at build time in conjunction with coho's x86_64_defconfig to generate a config for debug builds, and should replace the use of x86_64_debug_defconfig. Change-Id: I3fec9df07dd583796c2c4537d1369e40290a9023 Tracked-On: https://jira01.devtools.intel.com/browse/OAM-5220 Signed-off-by: Eric Ernst <eric.ernst@intel.com>