cmd: bootm: add a stage pre-load

Add a stage pre-load to the command bootm.
Right now, this stage may be used to read a
header and check the signature of the full
image.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 1d84012..7bd9546 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -194,6 +194,16 @@
 	help
 	  Boot an application image from the memory.
 
+config CMD_BOOTM_PRE_LOAD
+       bool "enable pre-load on bootm"
+       depends on CMD_BOOTM
+       depends on IMAGE_PRE_LOAD
+       default n
+       help
+         Enable support of stage pre-load for the bootm command.
+	 This stage allow to check or modify the image provided
+	 to the bootm command.
+
 config BOOTM_EFI
 	bool "Support booting UEFI FIT images"
 	depends on CMD_BOOTEFI && CMD_BOOTM && FIT