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/overo/config.mk b/board/overo/config.mk
index 59b651f..e7c471c 100644
--- a/board/overo/config.mk
+++ b/board/overo/config.mk
@@ -25,5 +25,4 @@
 # Linux-Kernel is expected to be at 8000'8000, entry 8000'8000
 # (mem base + reserved)
 
-# For use with external or internal boots.
-TEXT_BASE = 0x80008000
+CONFIG_SYS_TEXT_BASE = 0x80008000