payloads/LinuxBoot: Add ARM64 support

Add support for ARCH=ARM64 and introduce CROSS_COMPILE for all architectures.

* Always compress kernel Image using xz
* Create FIT uImage containing the kernel, initramfs and DTB
* Add ARM64 defconfig for all SoCs

Change-Id: I9a0cc248283432fb2384956ca55e687d4127398c
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/25152
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>

payloads/external/LinuxBoot/Kconfig

@@ -20,19 +20,30 @@ choice
 
 config LINUXBOOT_X86_64
 	bool "x86_64"
+	depends on ARCH_X86
 	help
 	  AMD64 kernel and initramfs
 
 config LINUXBOOT_X86
 	bool "x86"
+	depends on ARCH_X86
 	help
 	  X86 kernel and initramfs
+
+config LINUXBOOT_ARM64
+	bool "arm64"
+	depends on ARCH_ARM64
+	select PAYLOAD_FIT_SUPPORT
+	help
+	  AARCH64 kernel and initramfs
+
 endchoice
 
 config LINUXBOOT_ARCH
 	string
 	default "amd64" if LINUXBOOT_X86_64
 	default "386" if LINUXBOOT_X86
+	default "arm64" if LINUXBOOT_ARM64
 
 choice
 	prompt "Kernel version"
@@ -61,6 +72,11 @@ config LINUXBOOT_KERNEL_COMMANDLINE
 	help
 	  Add your own kernel command-line arguments.
 
+config LINUXBOOT_DTB_FILE
+	string "Compiled devicetree file"
+	depends on LINUXBOOT_ARM64
+	default ""
+
 config PAYLOAD_FILE
 	default "payloads/external/LinuxBoot/linuxboot/kernel-image"
 
@@ -106,8 +122,11 @@ config LINUXBOOT_UROOT_FILES
 	  initramfs.
 
 config PAYLOAD_USERSPACE
-	string ""
+	string "LinuxBoot initramfs"
 	default "payloads/external/LinuxBoot/linuxboot/initramfs.cpio.xz"
+	help
+	  The initramfs to use with the compiled kernel.
+	  Useful for debugging or custom initramfs.
 
 endif
 endif