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/bct-brettl2/config.mk b/board/bct-brettl2/config.mk
index dfd9456..0c02d44 100644
--- a/board/bct-brettl2/config.mk
+++ b/board/bct-brettl2/config.mk
@@ -24,7 +24,7 @@
 #
 
 # This is not actually used for Blackfin boards so do not change it
-#TEXT_BASE = do-not-use-me
+#CONFIG_SYS_TEXT_BASE = do-not-use-me
 
 CONFIG_BFIN_CPU = bf536-0.3