arm/arm64: ITS: Device and collection Initialization

Introduce an helper functions to register
- a new device, characterized by its device id and the
  max number of event IDs that dimension its ITT (Interrupt
  Translation Table).  The function allocates the ITT.

- a new collection, characterized by its ID and the
  target processing engine (PE).

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>