Correct the preprocessor directive used to check for 64-bit kernel support in the `zboot_go` function. The code previously checked for `CONFIG_X86_RUN_64BIT`, which is not the correct configuration option for determining if the kernel should run in 64-bit mode. The correct option is `CONFIG_X86_64`. Signed-off-by: Jeremy Compostella <jeremy.compostella@intel.com> Reviewed-by: Simon Glass <sjg@chromium.org>