build: Eliminate cutils/str_parms dependency from system/bt

Eliminate cutils/str_parmss dependency from system/bt by adding osi_str_parms:
 - Added hash_map_utils which implements partial functions of cutils/str_parms
   and uses osi/hash_map instead of cutils/hashmap.
 - Updated osi/Android.mk, osi/BUILD.gn and the includes in audio_a2dp to use
   osi_str_parms.
 - Added unittest for hash_map_utils.

Bug: 21957864
Change-Id: I8458d9e45df6cab2b71840d24d17b9d75de9842c