iio: stx104: Move to addac subdirectory

[ Upstream commit 955c2aa9cff2dd07ff798ca8c883398731687972 ]

The stx104 driver supports both ADC and DAC functionality.

Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
Link: https://lore.kernel.org/r/20220815222921.138945-1-william.gray@linaro.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Stable-dep-of: 4f9b80aefb9e ("iio: addac: stx104: Fix race condition when converting analog-to-digital")
Signed-off-by: Sasha Levin <sashal@kernel.org>