devkit8000: Move CONFIG_SYS_TEXT_BASE out of bss

This moves CONFIG_SYS_TEXT_BASE one MB after beginning of SD-RAM. Move
CONFIG_SYS_SPL_MALLOC_START to have one MB of free space for the u-boot
image.

CONFIG_SYS_TEXT_BASE was in the middle of the bss-section. This was the
reason for the problems with MMC boot described here:
http://article.gmane.org/gmane.comp.boot-loaders.u-boot/118711



Signed-off-by: Simon Schwarz <simonschwarzcor@gmail.com>
Tested-by: Thomas Weber <weber@corscience.de>
Signed-off-by: Tom Rini <trini@ti.com>