ACPI: NFIT: Install Notify() handler directly

Modify the ACPI NFIT driver to install its own Notify() handler directly
instead of providing an ACPI driver .notify() callback.

This will allow the ACPI driver .notify() callback to be eliminated.

Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com>
[ rjw: Subject and changelog edits, whitespace adjustments ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>