bootm: Add subcommands

Add the ability to break the steps of the bootm command into several
subcommands: start, loados, ramdisk, fdt, bdt, cmdline, prep, go.

This allows us to do things like manipulate device trees before
they are passed to a booting kernel or setup memory for a secondary
core in multicore situations.

Not all OS types support all subcommands (currently only start, loados,
ramdisk, fdt, and go are supported).

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/lib_blackfin/bootm.c b/lib_blackfin/bootm.c
index 9938ae5..195eb9c 100644
--- a/lib_blackfin/bootm.c
+++ b/lib_blackfin/bootm.c
@@ -36,6 +36,9 @@
 	int	(*appl) (char *cmdline);
 	char	*cmdline;
 
+	if ((flag != 0) && (flag != BOOTM_STATE_OS_GO))
+		return 1;
+
 #ifdef SHARED_RESOURCES
 	swap_to(FLASH);
 #endif