ratp: allow building without full console support ...

Make CONFIG_RATP a selectable config option, so that the user can
enable RATP support without explicitly needing to enable the full
console support over RATP (e.g. only for RATP FS or built-in command
support).

The full console can still be explicitly enabled with
CONFIG_CONSOLE_RATP.

Signed-off-by: Aleksander Morgado <aleksander@aleksander.es>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

ratp: moved logic to its own subdirectory ...

We are going to add new RATP command implementations in separate files
within this subdirectory.

Signed-off-by: Aleksander Morgado <aleksander@aleksander.es>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>