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/p2020ds/config.mk b/board/freescale/p2020ds/config.mk
index 4fcd69c..4268c19 100644
--- a/board/freescale/p2020ds/config.mk
+++ b/board/freescale/p2020ds/config.mk
@@ -23,8 +23,8 @@
 #
 # p2020ds board
 #
-ifndef TEXT_BASE
-TEXT_BASE = 0xeff80000
+ifndef CONFIG_SYS_TEXT_BASE
+CONFIG_SYS_TEXT_BASE = 0xeff80000
 endif
 
 RESET_VECTOR_ADDRESS = 0xeffffffc