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/board/hpe/gxp/Kconfig b/board/hpe/gxp/Kconfig
index 5b154a3..7536455 100644
--- a/board/hpe/gxp/Kconfig
+++ b/board/hpe/gxp/Kconfig
@@ -42,5 +42,5 @@
 config SYS_CONFIG_NAME
 	default "gxp"
 
-config SYS_TEXT_BASE
+config TEXT_BASE
 	default 0x50000000