Instead of rolling our own infrastructure to provide uniform access to I2C
and SPI buses, let's switch to using regmap.
Reviewed-by: Michael Hennerich <michael.hennerich@analog.com>
Tested-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>