iio:accel:mma8452: rework register definitions

Rework register definitions to be sorted by register and bit number, with
bit definitions cascaded under the appropriate register, use GENMASK for
consecutive bitmasks and realign properly.

Signed-off-by: Hartmut Knaack <knaack.h@gmx.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>