L2cap user dynamic channel: move psm alloc to bta am: a3eca176 am:...

L2cap user dynamic channel: move psm alloc to bta am: a3eca176 am: 9ea0cd35 am: ca5c812b am: d75cf9bf

Original change: https://android-review.googlesource.com/c/platform/system/bt/+/1443306

Change-Id: I52ecc67bd43bad1f262e8e39ee89c1d5dd73668d