adc: Move to using select in Kconfig for I2C & SPI busses

Move to using 'select SPI'/'select I2C' instead of 'depends on'
(see commit df81fef94483da9f2811d48088affbcfd61ab18c for more
 details)

Signed-off-by: Kumar Gala <galak@kernel.org>
4 files changed