[media] ts2020: re-implement PLL calculations

Used frequency synthesizer is simple Integer-N PLL, with configurable
reference divider, output divider and of course N itself. Old
calculations were working fine, but not so easy to understand.

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