ACPI / PM: Fix build for unusual combination of Kconfig options

CONFIG_PM_SLEEP may be set even if CONFIG_ACPI_SLEEP is unset,
although that is unusual.  For this reason, make the headers of
functions built for both CONFIG_ACPI and CONFIG_PM_SLEEP set
simultaneously depend on that combination of Kconfig options
instead of CONFIG_ACPI_SLEEP.

This fixes a build problem reported by Randy Dunlap.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>