drivers/iio/adc/cf_axi_adc: Fix SIGNEXTEND offset for AD9638

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
drivers/iio/adc/cf_axi_jesd204b: Add support for 1 and 2 lane setups

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>