V4L/DVB (6928): tda18271: break calculation functions out of tda18271_tune

Break out the following new functions from tda18271_tune:

tda18271_calc_bp_filter
tda18271_calc_km
tda18271_calc_rf_band
tda18271_calc_gain_taper
tda18271_calc_ir_measure
tda18271_calc_rf_cal

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>