ACPICA: Cleanup asmlinkage for ACPICA APIs.

Add an asmlinkage wrapper around acpi_enter_sleep_state() to prevent
an empty stub from being called by assmebly code for ACPI_REDUCED_HARDWARE
set.

As arch/x86/kernel/acpi/wakeup_xx.S is only compiled when CONFIG_ACPI=y
and there are no users of ACPI_HARDWARE_REDUCED, currently this is in
fact not a real issue, but a cleanup to reduce source code differences
between Linux and ACPICA upstream.

[rjw: Changelog]
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>