Staging: dt3155v4l: remove private memory allocator

This patch removes the private memory allocator
and all conjugated functions. Now the driver uses
videobuf-dma-contig module for allocations.
Added reserving 4MB coherent memory for private
per device allocations at probe time.

Signed-off-by: Marin Mitov <mitov@issp.bas.bg>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>