x86/kvm: Add static key for flush always

x86/kvm: Add static key for flush always

Avoid the conditional in the L1D flush control path.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Jiri Kosina <jkosina@suse.cz>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20180713142322.790914912@linutronix.de
Orabug: 28220674
CVE: CVE-2018-3646

(cherry picked from commit 4c6523ec59fe895ea352a650218a6be0653910b1)

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:
	arch/x86/kvm/vmx.c
Contextual: different content; Use unlikely(static_key_enabled) instead
of static_branch_unlikely because 11276d530 "locking/static_keys: Add a
new static_key interface" is not present in this version of kernel.