[media] tda8290: Allow custom std_map for tda18271

Allow specifying a custom std_map for tda18271 by external configuration.
This is required by cards that require custom std_map for analog TV or radio,
like AverMedia A706.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>