Testing repeat channels

[lucasrangit]

Add the rotation channel type to sample IIO dummy driver as an example of repeated channels. Also modify tools iio_info and iio_generic_buffer to test changes.

To test:

# setup iio device and trigger
sudo modprobe industrialio kfifo_buf industrialio-sw-trigger
sudo modprobe iio_dummy iio-trig-hrtimer
sudo mkdir /configfs
sudo mount -t configfs none /config
sudo mkdir /config/iio/triggers/hrtimer/instance1

# setup buffer
echo 1 > /sys/bus/iio/devices/iio\:device0/scan_elements/in_rot_quaternion_en
echo 1 > /sys/bus/iio/devices/iio\:device0/scan_elements/in_timestamp_en

# read from buffer
sudo ./generic_buffer -n iio_dummy_part_no -t instance1 -c 2
iio device number being used is 0
iio trigger number being used is 0
/sys/bus/iio/devices/iio:device0 instance1
30.000000 31.000000 32.000000 33.000000 1473803128573475241 
30.000000 31.000000 32.000000 33.000000 1473803128583472908