irqchip/gic-v3-its: Kill its->ite_size and use TYPER copy instead

Now that we have a copy of TYPER in the ITS structure, rely on this
to provide the same service as its->ite_size, which gets axed.
Errata workarounds are now updating the cached fields instead of
requiring a separate field in the ITS structure.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
Link: https://lore.kernel.org/r/20191027144234.8395-6-maz@kernel.org
Link: https://lore.kernel.org/r/20191108165805.3071-6-maz@kernel.org