input: misc: remove blackfin rotary driver

The blackfin architecture is getting removed, so this
one is obsolete as well.

Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Acked-by: Aaron Wu <aaron.wu@analog.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>