NOR/QSPI Flash on Layerscape board only has limited 64MB memory size.
Since some boards (ls1043ardb/ls1046ardb/ls1088ardb/ls1021atwr)
could support SD card boot, we added SD boot support for them to put
all things on SD card to meet large memory requirement.
Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
