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/README b/README
index 197804e..a52f3bf 100644
--- a/README
+++ b/README
@@ -2248,7 +2248,7 @@
 - CONFIG_SYS_MONITOR_BASE:
 		Physical start address of boot monitor code (set by
 		make config files to be same as the text base address
-		(TEXT_BASE) used when linking) - same as
+		(CONFIG_SYS_TEXT_BASE) used when linking) - same as
 		CONFIG_SYS_FLASH_BASE when booting from flash.
 
 - CONFIG_SYS_MONITOR_LEN: