seccomp: Move speculation migitation control to arch code

seccomp: Move speculation migitation control to arch code

The migitation control is simpler to implement in architecture code as it
avoids the extra function call to check the mode. Aside of that having an
explicit seccomp enabled mode in the architecture mitigations would require
even more workarounds.

Move it into architecture code and provide a weak function in the seccomp
code. Remove the 'which' argument as this allows the architecture to decide
which mitigations are relevant for seccomp.

OraBug: 28041771
CVE: CVE-2018-3639

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
(cherry picked from commit 8bf37d8c067bb7eb8e7c381bdadf9bd89182b6bc)
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
[Which is called bugs_64.c in UEK4]
	include/linux/nospec.h

[Which is called nospec-branch.h]

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