[media] e4000: revise synthesizer calculation

Update synthesizer calculation to model I prefer nowadays. It is
mostly just renaming some variables to ones I think are most standard.
Also add 'schematic' of synthesizer following my current understanding.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>