iio: adc: Kconfig: make AD9467 depend on ADI_AXI_ADC symbol

iio: adc: Kconfig: make AD9467 depend on ADI_AXI_ADC symbol

Because a dependency on HAS_IOMEM and OF was added for the ADI AXI ADC
driver, this makes the AD9467 driver have some build/dependency issues
when OF is disabled (typically on ACPI archs like x86).

This is because the selection of the AD9467 enforces the ADI_AXI_ADC symbol
which is blocked by the OF (and potentially HAS_IOMEM) being disabled.

To fix this, we make the AD9467 driver depend on the ADI_AXI_ADC symbol.
The AD9467 driver cannot operate on it's own. It requires the ADI AXI ADC
driver to stream data (or some similar IIO interface).

So, the fix here is to make the AD9467 symbol depend on the ADI_AXI_ADC
symbol. At some point this could become it's own subgroup of high-speed
ADCs.

Fixes: be24c65e9fa24 ("iio: adc: adi-axi-adc: add proper Kconfig dependencies")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Alexandru Ardelean <aardelean@deviqon.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20210324182746.9337-1-aardelean@deviqon.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>