diags: ddr: Don't corrupt barebox text

The DDR diags code used DRAM from 0 to 128 MB as scratch space. This
caused barebox to crash because it corrupted its own text and data
segment. Use the area between 256 and 512 MB instead.

Also, return 0 (for success) from Comcerto_ddr_test() to avoid
misleading error message.

Change-Id: I581e5c5b5bc4adf1cc43d9a378888bff530a3cee
2 files changed