cpu/hotplug: Boot HT siblings at least once

cpu/hotplug: Boot HT siblings at least once

Due to the way Machine Check Exceptions work on X86 hyperthreads it's
required to boot up _all_ logical cores at least once in order to set the
CR4.MCE bit.

So instead of ignoring the sibling threads right away, let them boot up
once so they can configure themselves. After they came out of the initial
boot stage check whether its a "secondary" sibling and cancel the operation
which puts the CPU back into offline state.

Reported-by: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Tony Luck <tony.luck@intel.com>
Orabug: 28220674
CVE: CVE-2018-3620

(cherry picked from commit 0cc3cd21657be04cb0559fe8063f2130493f92cf)

Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Conflicts:
	kernel/cpu.c
Contextual: The following changes were applied to the initial commit:
- used a per-cpu variable booted_once because struct cpuhp_cpu_state doesn't
exist in the current version
- cpu_smt_allowed check from bringup_wait_for_ap is done in _cpu_up
- taking into account that boot_cpu_state_init doesn't exist in the current
version (it was added by cff7d378: cpu/hotplug: Convert to a state machine
for the control processor), the per-cpu variable booted_once isn't made static
and it is set on true in start_kernel