data: add mappings for NeXTCube keyboard

Data referenced from

  https://github.com/spenczar/usb-next/blob/main/keymap.h

And cross-correlated with

  https://lists.nongnu.org/archive/html/qemu-devel/2024-10/msg05929.html

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>