V4L/DVB (7002): cx25840: Add basic CX23885 AVCore support

The cx23885/7/8 PCIe bridge has an internal AVCore modelled on
the cx2584x family. Many of the registers positions are identical
but some moved. The register values are also different because
the different bridges run at different clock rates.

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