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/sandbox_flattree_defconfig b/configs/sandbox_flattree_defconfig
index e18f9a0..01234dc 100644
--- a/configs/sandbox_flattree_defconfig
+++ b/configs/sandbox_flattree_defconfig
@@ -1,4 +1,4 @@
-CONFIG_SYS_TEXT_BASE=0
+CONFIG_TEXT_BASE=0
 CONFIG_NR_DRAM_BANKS=1
 CONFIG_ENV_SIZE=0x2000
 CONFIG_DEFAULT_DEVICE_TREE="sandbox"