ArmVirtPkg/FdtClientDxe: take DT node 'status' properties into account

ArmVirtPkg/FdtClientDxe: take DT node 'status' properties into account

DT has a [pseudo-]standardized 'status' property that can be set on
any node, and which signifies that a node should be treated as
absent unless it is set to 'ok' or 'okay'. So take this into account
when iterating over nodes.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>