LinuxBoot: refactor payload

Clean and refactor the structure of the LinuxBoot payload integration,
to make it more modular and readable. The kernel and initramfs should
handled in separated makefiles.

tested with:
- qemu-i440fx (x86, x86_64)
- cavium CN8100 (arm64)

Change-Id: I41d0275a5f7efb920e881f43b0acda29f41ee221
Signed-off-by: Marcello Sylvester Bauer <info@marcellobauer.com>
Reviewed-on: https://review.coreboot.org/c/29581
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>

payloads/external/LinuxBoot/arm64/kernel_fdt_lzma.its

@@ -45,20 +45,20 @@
 			};
 		};
 		ramdisk-1 {
-                        description = "Compressed Initramfs";
-                        data = /incbin/("initramfs.cpio.xz");
-                        type = "ramdisk";
-                        arch = "arm64";
-                        os = "linux";
-                        compression = "none";
-                        load = <00000000>;
-                        entry = <00000000>;
-                        hash-1 {
-                                algo = "sha1";
-                        };
-                        hash-2 {
-                                algo = "sha256";
-                        };
+			description = "Compressed Initramfs";
+			data = /incbin/("u-initramfs");
+			type = "ramdisk";
+			arch = "arm64";
+			os = "linux";
+			compression = "none";
+			load = <00000000>;
+			entry = <00000000>;
+			hash-1 {
+				algo = "sha1";
+			};
+			hash-2 {
+				algo = "sha256";
+			};
 		};
 	};