carma-fpga: drop videobuf dependency

This driver abuses videobuf helper functions. This is a bad idea
because:

1) this driver is completely unrelated to media drivers
2) the videobuf API is deprecated and will be removed eventually

This patch replaces the videobuf functions with the normal DMA kernel
API.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>