env: Rename env_driver_lookup_default and env_get_default_location

env: Rename env_driver_lookup_default and env_get_default_location

The env_driver_lookup_default and env_get_default_location functions are
about to get refactored to support loading from multiple environment.

The name is therefore not really well suited anymore. Drop the default
part to be a bit more relevant.

Reviewed-by: Andre Przywara <[email protected]>
Reviewed-by: Lukasz Majewski <[email protected]>
Reviewed-by: Simon Glass <[email protected]>
Signed-off-by: Maxime Ripard <[email protected]>