iio: adc: ti-adc081c: Partial revert of removal of ACPI IDs

Unfortuanately a non standards compliant ACPI ID is known to be
in the wild on some AAEON boards.

Partly revert the removal of these IDs so that ADC081C will again
work + add a comment to that affect for future reference.

Whilst here use generic firmware properties rather than the ACPI
specific handling previously found in this driver.

Reported-by: Kunyang Fan <Kunyang_Fan@aaeon.com.tw>
Fixes: c458b7ca ("iio:adc:ti-adc081c: Drop ACPI ids that seem very unlikely to be official.")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Tested-by: Kunyang Fan <Kunyang_Fan@aaeon.com.tw> #UP-extremei11
Link: https://lore.kernel.org/r/20211205172728.2826512-1-jic23@kernel.org
Cc: <Stable@vger.kernel.org>