msm: camera2: cpp: support deletion of mapped buffer entry

The CPP driver needs to support dynamic deletion of mapped
buffer when the stream is still active. This helps to flush
old mapped buffer entries from interferring in buffers which
reuse the buffer indices.

Change-Id: Ibe7379d3e5fa6c14890173eaf613b241630623ef
Signed-off-by: Rajakumar Govindaram <rajakuma@codeaurora.org>