ACPICA: Fix AcpiWalkNamespace race condition with table unload

Added a reader/writer locking mechanism to allow multiple
concurrent namespace walks (readers), but a dynamic table unload
will have exclusive access to the namespace. This fixes a problem
where a table unload could delete the portion of the namespace that
is currently being examined by a walk.  Adds a new file, utlock.c
that implements the reader/writer lock mechanism. ACPICA BZ 749.

http://www.acpica.org/bugzilla/show_bug.cgi?id=749

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/acpica/actables.h

@@ -79,7 +79,7 @@ void acpi_tb_delete_table(struct acpi_table_desc *table_desc);
 
 void acpi_tb_terminate(void);
 
-void acpi_tb_delete_namespace_by_owner(u32 table_index);
+acpi_status acpi_tb_delete_namespace_by_owner(u32 table_index);
 
 acpi_status acpi_tb_allocate_owner_id(u32 table_index);