V4L/DVB (7654): tda10086: make the xtal frequency a configuration option

Some DVB-S boards, i.e. with the SD1878 tuner, use a 4 MHz reference frequency.
This reqires a different setup of the clock PLL.
This patch adds an enum to the tda10086_config struct and sets the proper
values for the boards.

This patch also fixes the DVB-S section of the MD7134_BRIDGE_2

Signed-off-by: Hartmut Hackmann <hartmut.hackmann@t-online.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>