bootm: add prototype for arch_preboot_os

Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
diff --git a/include/bootm.h b/include/bootm.h
index 694d6fc..b3d1a62 100644
--- a/include/bootm.h
+++ b/include/bootm.h
@@ -54,4 +54,6 @@
 int do_bootm_states(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[],
 		    int states, bootm_headers_t *images, int boot_progress);
 
+void arch_preboot_os(void);
+
 #endif