Use the same file paths in both ISO and FAT

• In the FAT file system, the kernel and all initramfs images are in /EFI/archiso/.
• In the ISO, the kernel and main initramfs are in /arch/boot/x86_64/, and the microcode images are in /arch/boot/.

Presumably the file placement in FAT is because of UEFI specification (section 13.3.1.3): "All OS loaders and applications will be stored in subdirectories below EFI". Does the kernel qualify for that description (it does have CONFIG_EFI_STUB) or do we even care?

By using the same paths, the same boot loader configuration files could be used for both CD and USB.