x86/mwait-idle: Graceful probe failure when MWAIT is disabled

x86/mwait-idle: Graceful probe failure when MWAIT is disabled

When MWAIT is disabled, intel_idle refuses to probe.
But it may mis-lead the user by blaming this on the model number:

intel_idle: does not run on family 6 modesl 79

So defer the check for MWAIT until after the model# white-list check succeeds,
and if the MWAIT check fails, tell the user how to fix it:

intel_idle: Please enable MWAIT in BIOS SETUP

Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
[Linux commit: a4c447533a18ee86e07232d6344ba12b1f9c5077]
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>