x86/idle: rework C6 EOI workaround

x86/idle: rework C6 EOI workaround

Change the C6 EOI workaround (errata AAJ72) to use x86_match_cpu. Also
call the workaround from mwait_idle, previously it was only used by
the ACPI idle driver. Finally make sure the routine is called for all
states equal or greater than ACPI_STATE_C3, note that the ACPI driver
doesn't currently handle them, but the errata condition shouldn't be
limited by that.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>