common: fit: Add weak board_fit_config_name_match

Several architectures had a default board_fit_config_name_match already;
this provides a generic weak version. We default to rejecting all configs.
This will use the FIT's default config, instead of the first config. This
may result in boot failures if there are multiple configurations and the
first config is *not* the default.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>