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/doc/arch/sandbox.rst b/doc/arch/sandbox.rst
index 068d4a3..ed66f70 100644
--- a/doc/arch/sandbox.rst
+++ b/doc/arch/sandbox.rst
@@ -619,5 +619,5 @@
   f0000   CONFIG_PRE_CON_BUF_ADDR    Pre-console buffer
  100000   CONFIG_TRACE_EARLY_ADDR    Early trace buffer (if enabled). Also used
                                      as the SPL load buffer in spl_test_load().
- 200000   CONFIG_SYS_TEXT_BASE       Load buffer for U-Boot (sandbox_spl only)
+ 200000   CONFIG_TEXT_BASE           Load buffer for U-Boot (sandbox_spl only)
 =======   ========================   ===============================