This adds support for initializing DDR3 RAMs on the i.MX53 type
SDRAM controller. The code automatically detects size/layout of
the connected RAM, detects the bus width and which chipselects are
populated.
While I believe this code is not 100% generic, it is far too
sophisticated to stay in a single board directory. I'm sure
other boards could make use of this aswell.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>