[media] dvb-frontends/stv0367: make PLLSETUP a function, add 58MHz IC speed

This moves the PLL SETUP code from stv0367ter_init() into a dedicated
function, and also make it possible to configure 58Mhz IC speed at
27MHz Xtal (used on STV0367-based DDB cards/modules in QAM mode).

Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>