x86/bugs: Unify x86_spec_ctrl_{set_guest,restore_host}

x86/bugs: Unify x86_spec_ctrl_{set_guest,restore_host}

Function bodies are very similar and are going to grow more almost
identical code. Add a bool arg to determine whether SPEC_CTRL is being set
for the guest or restored to the host.

No functional changes.

Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Orabug: 28063992
CVE: CVE-2018-3639

(cherry picked from commit cc69b349)
Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Conflicts:
	arch/x86/kernel/cpu/bugs.c
[Different filename bugs_64.c]

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