arm: mvebu: clearfog: document boot from SATA

Document the main U-Boot image offset when booting from SATA disk on the
Clearfog board.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Stefan Roese <sr@denx.de>
1 file changed