Add CONFIG_SYS_SYM_OFFSETS to support offset symbols

Link symbols as created by the link script can either be absolute or
relative to the text start. This option switches between the two options
so that we can support both.

As we convert architectures over to generic board, we can see if this
option is actually needed, or whether it is possible to unify this feature
also.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/README b/README
index bdce275..a620f0a 100644
--- a/README
+++ b/README
@@ -3222,6 +3222,13 @@
 	its config.mk file). If you find problems enabling this option on
 	your board please report the problem and send patches!
 
+- CONFIG_SYS_SYM_OFFSETS
+	This is set by architectures that use offsets for link symbols
+	instead of absolute values. So bss_start is obtained using an
+	offset _bss_start_ofs from CONFIG_SYS_TEXT_BASE, rather than
+	directly. You should not need to touch this setting.
+
+
 The following definitions that deal with the placement and management
 of environment data (variable area); in general, we support the
 following configurations: