staging: adis16255 - TODO issues resolved and typos removed

This patch adds the adis16255 driver to the build system under the staging directory.
It solves also most issues mentioned in TODO list:
- sample rate exported to sysfs
- spi_adis16255_bringup and spi_adis16255_shutdown encapsulated
- chip selftest in spi_adis16255_bringup
- kernel messages reduced to a reasonable number
I removed the TODO file, because ther was only the reset of the gyroscope left.
This is IMOH not necessary for the actual driver.

There are also some typos in adis.c file. This patch should get rid of them as well.

Signed-off-by: Matthias Brugger <mensch0815@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>