alpha: Implement CPU vulnerabilities sysfs functions.

Implement the CPU vulnerabilty show functions for meltdown, spectre_v1
and spectre_v2 on Alpha.

Tests on XP1000 (EV67/667MHz) and ES45 (EV68CB/1.25GHz) show them
to be vulnerable to Meltdown and Spectre V1.  In the case of
Meltdown I saw a 1 to 2% success rate in reading bytes on the
XP1000 and 50 to 60% success rate on the ES45. (This compares to
99.97% success reported for Intel CPUs.)  Report EV6 and later
CPUs as vulnerable.

Tests on PWS600au (EV56/600MHz) for Spectre V1 attack were
unsuccessful (though I did not try particularly hard) so mark EV4
through to EV56 as not vulnerable.

Signed-off-by: Michael Cree <mcree@orcon.net.nz>
Signed-off-by: Matt Turner <mattst88@gmail.com>
diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index e96adcb..b202288 100644
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig
@@ -18,6 +18,7 @@
 	select ARCH_HAVE_NMI_SAFE_CMPXCHG
 	select AUDIT_ARCH
 	select GENERIC_CLOCKEVENTS
+	select GENERIC_CPU_VULNERABILITIES
 	select GENERIC_SMP_IDLE_THREAD
 	select GENERIC_STRNCPY_FROM_USER
 	select GENERIC_STRNLEN_USER