ACPICA: Add text: ACPICA policy for new _OSI strings. No functional change.

Adds further information about why new _OSI strings should be
adopted by all hosts as soon as possible.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>