acpi: Tell SMM we will handle CPPC notifications

Buggy SMM implementations can hang while processing CPPC notifications.
This leads to some laptops (notably Thinkpads) hanging when the
hwpstate_intel driver is loaded.

Tell the SMM that we will handle CPPC notifications as described in:

• Intel® Processor Vendor-Specific ACPI
• Intel® 64 and IA-32 Architectures Software Developer’s Manual

CPPC events default to masked (disabled) so while we do not do any
handling right now this does not seem to lead to any issues.

This approach was found via this Linux Kernel patch:
https://lkml.org/lkml/2016/3/17/563

PR: 253288
Reviewed by: imp, jhb
Sponsored by: Modirum
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D36699

(cherry picked from commit 67f2a563bfcad75c16536ca500b06ddc9306dfa0)
(cherry picked from commit eee0f7aea42564fe005c74f004d63f8cc170ef59)
(cherry picked from commit 15bd2f366d3e878f5a8bc1628368d59ef318af5f)