prctl: Add force disable speculation

prctl: Add force disable speculation

For certain use cases it is desired to enforce mitigations so they cannot
be undone afterwards. That's important for loader stubs which want to
prevent a child from disabling the mitigation again. Will also be used for
seccomp(). The extra state preserving of the prctl state for SSB is a
preparatory step for EBPF dymanic speculation control.

OraBug: 28041771
CVE: CVE-2018-3639

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
(cherry picked from commit 356e4bfff2c5489e016fdb925adbf12a1e3950ee)
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
 Conflicts:
	arch/x86/kernel/cpu/bugs.c

[File is called bugs_64.c]
	include/linux/sched.h

Signed-off-by: Brian Maly <brian.maly@oracle.com>