fpga: zynqmp: support loading authenticated images

Add supporting new compatible string "u-boot,zynqmp-fpga-ddrauth" to
handle loading authenticated images (DDR).

Based on solution by Jorge Ramirez-Ortiz <jorge@foundries.io>

Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>
Tested-by: Ricardo Salveti <ricardo@foundries.io>
Link: https://lore.kernel.org/r/20220722141614.297383-13-oleksandr.suvorov@foundries.io
Signed-off-by: Michal Simek <michal.simek@amd.com>
diff --git a/boot/Kconfig b/boot/Kconfig
index 17438b5..59d0c65 100644
--- a/boot/Kconfig
+++ b/boot/Kconfig
@@ -210,8 +210,8 @@
 	  1. "loadables" images, other than FDTs, which do not have a "load"
 	     property will not be loaded. This limitation also applies to FPGA
 	     images with the correct "compatible" string.
-	  2. For FPGA images, only the "compatible" = "u-boot,fpga-legacy"
-	     loading method is supported.
+	  2. For FPGA images, the supported "compatible" list is in the
+	     doc/uImage.FIT/source_file_format.txt.
 	  3. FDTs are only loaded for images with an "os" property of "u-boot".
 	     "linux" images are also supported with Falcon boot mode.