staging:iio: allow channels to be set up using a table of iio_channel_spec structures.

V8: Add missing address in IIO_CHAN macro. Spotted by Michael Hennerich.
V7: Document additions to iio_dev structure.
V6: Fixup the docs for iio_chan_spec structure.
V5: Actually have the macro handle the _input type channels (oops)
V4: Add ability to do, _input and modified channel naming in a coherent fashion.
    Scrap all the messy IIO_CHAN_* macros and move to only one.

V3: Added more types - intensity and light.

V2: Various fixes - some thanks to Arnd.
    Bug fix for unregistering of event attr group
    Changed iio_read_channel_info to have two part value - use for
    raw value read as well.
    constify the channelspec structures
    raw write support for calibbias and similar
    Additional strings for buidling attribute names.

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>