config, x86 enable boot cpu hotplug
    
    Set CONFIG_BOOTPARAM_HOTPLUG_CPU0 to 'y'.  Currently, to disable CPU0,
    the "boot" cpu, one must specify cpu0_hotplug as a kernel parameter.
    Setting this config variable to 1 enables it by default.
    
    I've tested this on systems where it was expected to work and it seems to
    function properly.
    
    Signed-off-by: Prarit Bhargava <prarit@redhat.com>