bootstd: Allow bootmeths to be marked as global

The current way of handling things like EFI bootmgr is a bit odd, since
that bootmeth handles selection of the bootdev itself. VBE needs to work
the same way, so we should support it properly.

Add a flag that indicates that the bootmeth is global, rather than being
invoked on each bootdev. Provide a helper to read a bootflow from the
bootmeth.

Signed-off-by: Simon Glass <sjg@chromium.org>

cmd/bootmeth.c

@@ -69,7 +69,9 @@ static int do_bootmeth_list(struct cmd_tbl *cmdtp, int flag, int argc,
 			}
 		}
 
-		if (order == -1)
+		if (ucp->flags & BOOTMETHF_GLOBAL)
+			printf("%5s", "glob");
+		else if (order == -1)
 			printf("%5s", "-");
 		else
 			printf("%5x", order);