spl: Add an arch-specific hook for writing to SPL handoff

At present there is an arch-specific area in the SPL handoff area intended
for use by arch-specific code, but there is no explicit call to fill in
this data. Add a hook for this.

Also use the hook to remove the sandbox-specific test code from
write_spl_handoff().

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/include/handoff.h b/include/handoff.h
index aacb0f5..75d19b1 100644
--- a/include/handoff.h
+++ b/include/handoff.h
@@ -31,6 +31,19 @@
 void handoff_save_dram(struct spl_handoff *ho);
 void handoff_load_dram_size(struct spl_handoff *ho);
 void handoff_load_dram_banks(struct spl_handoff *ho);
+
+/**
+ * handoff_arch_save() - Save arch-specific info into the handoff area
+ *
+ * This is defined to an empty function by default, but arch-specific code can
+ * define it to write to spi_handoff->arch. It is called from
+ * write_spl_handoff().
+ *
+ * @ho: Handoff area to fill in
+ * @return 0 if OK, -ve on error
+ */
+int handoff_arch_save(struct spl_handoff *ho);
+
 #endif
 
 #endif