kernel.mk: build dtb for architecture that support it.
kernel.mk: build dtb for architecture that support it.

And only for those ones:
 * arc,
 * arm/arm64,
 * c6x,
 * h8300,
 * metag,
 * microblaze,
 * nios2,
 * openrisc,
 * powerpc,
 * sparc.

Signed-off-by: Gaël PORTAY <1666f60cfa201a60b0ea694168a0b6932673170a@gmail.com>

gazoo74/initramfs,gazoo74/initramfs