Rename CONFIG_SYS_TEXT_BASE to CONFIG_TEXT_BASE

The current name is inconsistent with SPL which uses CONFIG_SPL_TEXT_BASE
and this makes it imposible to use CONFIG_VAL().

Rename it to resolve this problem.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/mscc_luton_defconfig b/configs/mscc_luton_defconfig
index 15339d4..30f7802 100644
--- a/configs/mscc_luton_defconfig
+++ b/configs/mscc_luton_defconfig
@@ -1,5 +1,5 @@
 CONFIG_MIPS=y
-CONFIG_SYS_TEXT_BASE=0x40000000
+CONFIG_TEXT_BASE=0x40000000
 CONFIG_SYS_MALLOC_LEN=0x1f0000
 CONFIG_ENV_SIZE=0x2000
 CONFIG_ENV_OFFSET=0x100000