x86/ACPI: CPPC: Add missing include

Some minimial kernel configurations will fail with -Werror=implicit-function-declaration
due to a missing header include.

Add that header.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://patch.msgid.link/20250211203314.762755-1-superm1@kernel.org


[ rjw: Subject edit ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>