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/qemu-ppce500_defconfig b/configs/qemu-ppce500_defconfig
index 4e2e77a..351913f 100644
--- a/configs/qemu-ppce500_defconfig
+++ b/configs/qemu-ppce500_defconfig
@@ -1,5 +1,5 @@
 CONFIG_PPC=y
-CONFIG_SYS_TEXT_BASE=0xf00000
+CONFIG_TEXT_BASE=0xf00000
 CONFIG_ENV_SIZE=0x2000
 CONFIG_DEFAULT_DEVICE_TREE="qemu-ppce500"
 CONFIG_SYS_CLK_FREQ=33000000