irqchip/irq-gic-v3-its.c: Force synchronisation when issuing INVALL

INVALL CMD specifies that the ITS must ensure any caching associated with
the interrupt collection defined by ICID is consistent with the LPI
configuration tables held in memory for all Redistributors. SYNC is
required to ensure that INVALL is executed.

Currently, LPI configuration data may be inconsistent with that in the
memory within a short period of time after the INVALL command is executed.

Signed-off-by: Wudi Wang <wangwudi@hisilicon.com>
Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Fixes: cc2d3216 ("irqchip: GICv3: ITS command queue")
Link: https://lore.kernel.org/r/20211208015429.5007-1-zhangshaokun@hisilicon.com