Rename TEXT_BASE into CONFIG_SYS_TEXT_BASE

The change is currently needed to be able to remove the board
configuration scripting from the top level Makefile and replace it by
a simple, table driven script.

Moving this configuration setting into the "CONFIG_*" name space is
also desirable because it is needed if we ever should move forward to
a Kconfig driven configuration system.

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/board/dbau1x00/README b/board/dbau1x00/README
index b37ff36..b1e9494 100644
--- a/board/dbau1x00/README
+++ b/board/dbau1x00/README
@@ -26,7 +26,7 @@
 
 NOTE! When you switch between the two boot flashes, the
 base addresses will be swapped.
-Have this in mind when you compile u-boot. TEXT_BASE has
+Have this in mind when you compile u-boot. CONFIG_SYS_TEXT_BASE has
 to match the address where u-boot is located when you
 actually launch.