Build Image.gz

Note, that currently BBL and OpenSBI would require manually
uncompressing it for usage. U-boot will support compressed kernel
payloads.

Signed-off-by: David Abdurachmanov <david.abdurachmanov@gmail.com>

kernel.spec

@@ -313,9 +313,8 @@ Summary: The Linux kernel
 %define all_arch_configs kernel-%{version}-riscv64*.config
 %define asmarch riscv
 %define hdrarch riscv
-%define make_target vmlinux
-%define kernel_image vmlinux
-%define kernel_image_elf 1
+%define make_target Image.gz
+%define kernel_image arch/riscv/boot/Image.gz
 %endif