ARM: atmel: Enable FIT image support for SAMA5Dx

ARM: atmel: Enable FIT image support for SAMA5Dx

Enable the fitImage support for the entire SAMA5Dx lineup of CPUs.
The fitImage is superior image format to uImage and it is useful
to have it available.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Andreas Bießmann <andreas.devel@googlemail.com>
Cc: Wenyou Yang <wenyou.yang@atmel.com>
Reviewed-by: Andreas Bießmann <andreas@biessmann.org>
[rebase on current ToT]
Signed-off-by: Andreas Bießmann <andreas@biessmann.org>