V4L/DVB (6155): Cleanup/remove code to access the sram memory maps

The cx23885 and cx23887 family use two different memory maps which govern
how the internal SRAM is configured. This patch streamlines the access to those
structures.

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