[media] af9013: convert to regmap api

Use regmap for register access. Own low level i2c read and write
routines for regmap is still needed because chip uses single command
byte in addition to typical i2c register access.

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