ACPI / PM: Fix build problems for !CONFIG_ACPI related to NVS rework

The recent rework of the NVS saving/restoring code introduced two
build issues for !CONFIG_ACPI, a warning in drivers/acpi/internal.h
and an error in arch/x86/kernel/e820.c.

Fix them by providing suitable static inline definitions of the
relevant functions.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Len Brown <len.brown@intel.com>