V4L/DVB (7464): Convert driver to use a single SRAM memory map

This reduces the memory footprint and removes the need to
manually configure each map, which lead to a bug where
the Fusion EXP 5 board broke for a while.
This also fixes digital support again for
the DViCO FusionHDTV5Express.

Signed-off-by: Steven Toth <stoth@hauppauge.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>