staging: iio: ad9832: remove platform_data support

staging: iio: ad9832: remove platform_data support

Remove legacy platform_data support as there are no in tree users and
this approach belongs to a long gone era. The policy decision on what
to output is a userspace problem, not something that should be provided
from firmware.

The driver now initializes the device to a safe state (SLEEP|RESET|CLR)
outputting nothing. Userspace can configure the desired frequencies and
phases via the existing sysfs attributes once the device is ready to be
used.

Original discussion started here [1].

Link: https://lore.kernel.org/linux-iio/20250628161040.3d21e2c4@jic23-huawei/
Suggested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Tomas Borquez <tomasborquez13@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>