ART: Handle Extended MIRs in a uniform manner

The special handling is needed since some extended MIRs can hold values in
args array, and we might want to handle the dataflow for those in a
specialized manner. Current dataflow attributes may not be able to describe
it for the extended MIRs.

Change-Id: I8b64f3142a4304282bb31f1d4686eba72284d97d
Signed-off-by: Jean Christophe Beyler <jean.christophe.beyler@intel.com>
Signed-off-by: Udayan Banerji <udayan.banerji@intel.com>