mwait-idle: prevent SKL-H boot failure when C8+C9+C10 enabled

mwait-idle: prevent SKL-H boot failure when C8+C9+C10 enabled

Some SKL-H configurations require "max_cstate=7" to boot.
While that is an effective workaround, it disables C10.

This patch detects the problematic configuration,
and disables C8 and C9, keeping C10 enabled.

Note that enabling SGX in BIOS SETUP can also prevent this issue,
if the system BIOS provides that option.

https://bugzilla.kernel.org/show_bug.cgi?id=109081
"Freezes with Intel i7 6700HQ (Skylake), unless intel_idle.max_cstate=7"

Signed-off-by: Len Brown <len.brown@intel.com>
[Linux commit: d70e28f57e14a481977436695b0c9ba165472431]

Adjust to Xen infrastructure.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>