ACPI 5.0: Allow _AEI method in walk resources

_AEI contains a resource template, this change adds support for
the walk resources function.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
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>