media: dvb: mpq: TSPP output buffer allocation by demux plugin

The TSPP driver can allocate its output buffers internally or
externally. External buffer allocation is required when Demux wishes
to use the ION driver to allocate a physically contiguous buffer
(e.g. to pass to TZ).
This commit improves the TSPP driver support for external buffer
allocation and implements the external memory allocation and free
functions in the Demux driver.

Change-Id: Id7e815fa56b76401ed593a786eb61d97735deba9
Signed-off-by: Liron Kuch <lkuch@codeaurora.org>
Signed-off-by: Neha Pandey <nehap@codeaurora.org>