ACPICA: Linux: Allow ACPICA inclusion for CONFIG_ACPI=n builds.

This patch moves <acpi/acpi.h> out of CONFIG_ACPI condition so that all
ACPICA prototypes can be seen by the CONFIG_ACPI=n Linux kernel builds.
Note that we can do this because ACPICA has implemented stubs for all
ACPICA prototypes that are currently referenced by the Linux kernel.

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