Input: ams_delta_serio: convert to platform driver

Convert the driver to an "ams-delta-serio" platform driver.  For it to
be used with Amstrad Delta, register an "ams-delta-serio" platform
device from the board init file.

Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>