iio: ABI: fix correctness of I and Q modifiers

Update the IIO ABI documentation to reflect the actual usage of channels
with I and Q modifiers. These are currently only used in a few drivers:

frequency/admv1013 (kernel v5.17):
- in_altvoltageY-altvoltageZ_i_calibphase
- in_altvoltageY-altvoltageZ_q_calibphase
- in_altvoltageY_i_calibbias
- in_altvoltageY_q_calibbias
frequency/admv1014 (kernel v5.18):
- in_altvoltageY_i_phase
- in_altvoltageY_q_phase
- in_altvoltageY_i_offset
- in_altvoltageY_q_offset
- in_altvoltageY_i_calibscale_course
- in_altvoltageY_i_calibscale_fine
- in_altvoltageY_q_calibscale_course
- in_altvoltageY_q_calibscale_fine
frequency/adrf6780 (kernel v5.16):
- out_altvoltageY_i_phase
- out_altvoltageY_q_phase

There are no _raw or _scale attributes in use, so those are all removed.
There are no currentY attributes in use with these modifiers, so those
are also removed. All of the voltageY are changed to altvoltageY since
that is how they are actually used. None of these channels are used
with scan buffers, so all of those attributes are removed as well. And
the {in,out}_altvoltageY_{i,q}_phase attributes were missing so those
are added.

The differential channel names for admv1013 are fixed.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250711-iio-abi-fix-i-and-q-modifiers-v1-1-35963c9c8c01@baylibre.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>