This new memtest can test the whole unused memory. The new memtest
command try to request the whole unused sdram regions on all banks and
run the mem_test routine from common/memtest.c on it.

The memtest command has only two parameters;
  -i	Amount of iterations, default 1, iteration of 0 is endless.
  -b	Set this to skip integrity check.(Do only a fast test for bus lines)

If MMU support is enable, memtest try to run memtest twice. The first with
cache enabled, the second with cache disabled.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>