iio: adc: meson-saradc: Disable BL30 integration on G12A and newer SoCs

iio: adc: meson-saradc: Disable BL30 integration on G12A and newer SoCs

G12A and newer don't use the SAR ADC to read the SoC temperature from
within the firmware. Instead there's now a dedicated thermal sensor.
Disable the BL30 integration for G12A and newer SoCs to save a few CPU
cycles when reading samples.
Adding a separate struct meson_sar_adc_data is a good idea anyways
because starting with G12A there's some extra registers to read the
samples in a simplified way.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20210717233718.332267-2-martin.blumenstingl@googlemail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>