x86/defconfig: Enable CONFIG_DEBUG_ENTRY=y

A bug was recently found via CONFIG_DEBUG_ENTRY=y, and the x86
tree kinda is the main source of changes to the x86 entry code,
so enable this debug option by default in our defconfigs.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: linux-kernel@vger.kernel.org