bootm: refactor do_reset and os boot function args

There is no need for each OS specific function to call do_reset() we
can just do it once in bootm. This means its feasible on an error for
the OS boot function to return.

Also, remove passing in cmd_tbl_t as its not needed by the OS boot
functions.  flag isn't currently used but might be in the future so
we left it alone.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/lib_nios/bootm.c b/lib_nios/bootm.c
index fb2e9b5..b0d5b82 100644
--- a/lib_nios/bootm.c
+++ b/lib_nios/bootm.c
@@ -28,7 +28,7 @@
  * we can get this working. ;-)
  *
  */
-void do_bootm_linux(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[],
-		bootm_headers_t *images)
+int do_bootm_linux(int flag, int argc, char *argv[], bootm_headers_t *images)
 {
+	return 1;
 }