proc: Provide details on speculation flaw mitigations

proc: Provide details on speculation flaw mitigations

As done with seccomp and no_new_privs, also show speculation flaw
mitigation state in /proc/$pid/status.

OraBug: 28041771
CVE: CVE-2018-3639

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
(cherry picked from commit fae1fa0fc6cca8beee3ab8ed71d54f9a78fa3f64)
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
 Conflicts:
	fs/proc/array.c
[Missing seq_putc]

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