iio: adc: adi-axi-adc: add proper Kconfig dependencies

iio: adc: adi-axi-adc: add proper Kconfig dependencies

The ADI AXI ADC driver requires IO mem access and OF to work. This change
adds these dependencies to the Kconfig symbol of the driver.

This was also found via the lkp bot, as the
devm_platform_ioremap_resource() symbol was not found at link-time on the
S390 architecture.

Fixes: ef04070692a21 ("iio: adc: adi-axi-adc: add support for AXI ADC IP core")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Cc: <Stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210210105044.48914-1-alexandru.ardelean@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>