spl: Add full fitImage support

Add support for loading U-Boot and optionally FDT from a fitImage
in SPL by using the full fitImage support from U-Boot. While we do
have limited SPL loading support in SPL with a small footprint, it
is missing a lot of important features, like checking signatures.
This support has all the fitImage features, while the footprint is
obviously larger.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/Kconfig b/Kconfig
index 7d9e971..5a82c95 100644
--- a/Kconfig
+++ b/Kconfig
@@ -328,6 +328,17 @@
 	  particular it can handle selecting from multiple device tree
 	  and passing the correct one to U-Boot.
 
+config SPL_LOAD_FIT_FULL
+	bool "Enable SPL loading U-Boot as a FIT"
+	select SPL_FIT
+	help
+	  Normally with the SPL framework a legacy image is generated as part
+	  of the build. This contains U-Boot along with information as to
+	  where it should be loaded. This option instead enables generation
+	  of a FIT (Flat Image Tree) which provides more flexibility. In
+	  particular it can handle selecting from multiple device tree
+	  and passing the correct one to U-Boot.
+
 config SPL_FIT_IMAGE_POST_PROCESS
 	bool "Enable post-processing of FIT artifacts after loading by the SPL"
 	depends on SPL_LOAD_FIT