ART: Initialization of RegLocation and API for GrowableArray Iterator

Two things:

- Added a default initialization for the RegLocation.
- Added a default constructor and Reset for the GrowableArray's Iterator class.

Change-Id: I74d9c584304c77add42e0d66e4037ac45b890142
Signed-off-by: Jean Christophe Beyler <jean.christophe.beyler@intel.com>
Signed-off-by: Razvan A Lupusoru <razvan.a.lupusoru@intel.com>
Signed-off-by: Yixin Shou <yixin.shou@intel.com>
Signed-off-by: Chao-ying Fu <chao-ying.fu@intel.com>
Signed-off-by: Udayan Banerji <udayan.banerji@intel.com>