arm64: Print DT machine model in setup_machine_fdt()

On arm32, the machine model specified in the device tree is printed
during boot-up, courtesy of of_flat_dt_match_machine().

On arm64, of_flat_dt_match_machine() is not called, and the machine
model information is not available from the kernel log.

Print the machine model to make it easier to derive the machine model
from an arbitrary kernel boot log.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>