ACPI: processor: idle: Expose max_cstate/nocst/bm_check_disable read-only in sysfs

This will allow super users to verify the module parameters in question
when changed via kernel command line.

The parameters "nocst/bm_check_disable" are only used for enable/disable,
so change them from integer to bool.

Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
[ rjw: Changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>