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/freescale/m54451evb/config.mk b/board/freescale/m54451evb/config.mk
index b42fcc9..4ed60f2 100644
--- a/board/freescale/m54451evb/config.mk
+++ b/board/freescale/m54451evb/config.mk
@@ -24,4 +24,4 @@
 
 sinclude $(OBJTREE)/board/$(BOARDDIR)/config.tmp
 
-PLATFORM_CPPFLAGS += -DTEXT_BASE=$(TEXT_BASE)
+PLATFORM_CPPFLAGS += -DCONFIG_SYS_TEXT_BASE=$(CONFIG_SYS_TEXT_BASE)