msm: camera_v2: Use stream cnt for unique stream id

Add new atomic counter for keeping track of stream counts.
The exisitng open_cnt counter is not full-proff since there could
be multiple streams with the stream id in the folowing
scenario:
a) Create stream 1, 2, and 3
b) Destroy stream 2
c) Add new stream; will result in another stream with id 3.

CRs-fixed: 493632
Change-Id: Icfa3cb2fd2c34c6da7e5f09d016fef4577331264
Signed-off-by: Ankit Premrajka <ankitp@codeaurora.org>