drivers: Add cellular API for network configuration

Adds two APIs which allow for configuring the cellular
network configuration of a cellular network device. like
a cellular modem. The first allows for configuring which
access technology to use, and optionally, which bands to
use. The second allows for getting all supported access
technologies are supported, and which bands for each tech
are supported.

Signed-off-by: Bjarki Arge Andreasen <bjarkix123@gmail.com>