staging:iio:accel:sca3000 merge files into one.

In the early days of IIO we were much more inclined to keep the impact
of the core IIO elements to the minimum.  As time has moved on it has
become clear that hardly any builds are done without buffer support
and that it adds considerable complexity to the drivers.

Hence merge down the buffer and non buffer elements of the sca3000 driver
also allowing us to drop the header file used for the interfaces between
the two.

Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>