Input: bfin_rotary - use generic IO functions

Instead of using arch-specific accessors remap rotary register physical
address into kernel space in probe and use standard readw and writew to
access rotary MMRs.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>