uboot-imx

i.MX28: Implement boot pads sampling and reporting

This patch implements code that samples i.MX28 boot pads and reports boot mode
accordingly.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Detlev Zundel <dzu@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Wolfgang Denk <wd@denx.de>