Features supported :
* Serial console
* SPI Flash
* MMC/SD Card
* eMMC storage
* SATA
* PCA9555 - GPIO expander over I2C5 bus
* USB
Use spl alternate boot device feature to define fallback to
the main boot device as it is defined by hardware.
Signed-off-by: Dmitry Lifshitz
[uri.mashiach@compulab.co.il: Adjust to v2016.11]
Signed-off-by: Uri Mashiach
Acked-by: Igor Grinberg