We can detect the SDRAM automatically, no need to let the boards
do it manually.
This also fixes device tree based i.MX28 boards like the duckbill.
These boards once had a /memory node in the device tree, but now
that this was changed to /memory@40000000 barebox didn't find it
anymore.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Tested-by: Roland Hieber <r.hieber@pengutronix.de>
Signed-off-by: Roland Hieber <r.hieber@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>