mtd: dataflash: Say if we find a device we don't support

Ensure that the error message if we identify a flash we don't know how to
talk to is displayed on the console in order to aid diagnostics. While
we're at convert the message to use dev_info() rather than our hand rolled
version of it for consistency.

Signed-off-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>