Introduce `USE_EXP_X86_64_SUPPORT` in `src/arch/x86/Kconfig` and guard it with `HAVE_EXP_X86_64_SUPPORT`. Replace the per-CPU implementations of the same functionality with the newly-added Kconfig options. Update documentation and the config file for QEMU accordingly. Change-Id: I550216fd2a8323342d6b605306b0b95ffd5dcd1c Signed-off-by: Angel Pons <th3fanbus@gmail.com> Reviewed-on: https://review.coreboot.org/c/coreboot/+/55760 Tested-by: build bot (Jenkins) <no-reply@coreboot.org> Reviewed-by: Patrick Rudolph <siro@das-labor.org>