xen/arm: gic: GICv2 & GICv3 only supports 1020 physical interrupts

xen/arm: gic: GICv2 & GICv3 only supports 1020 physical interrupts

GICD_TYPER.ITLinesNumber can encode up to 1024 interrupts. Although,
IRQ 1020-1023 are reserved for special purpose.

The result is used by the callers of gic_number_lines in order to check
the validity of an IRQ.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Cc: Frediano Ziglio <frediano.ziglio@huawei.com>
Cc: Zoltan Kiss <zoltan.kiss@huawei.com>