Add a default for TPL_TEXT_BASE

If this value is not provided it causes a hang in the build. Add a default
value to avoid this.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/Kconfig b/common/spl/Kconfig
index dc319ad..a3a6f31 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -1412,6 +1412,7 @@
 
 config TPL_TEXT_BASE
 	hex "Base address for the .text section of the TPL stage"
+	default 0
 	help
 	  The base address for the .text section of the TPL stage.