KVM: arm64: vgic-v4: Restore pending state on host userspace write

When the VMM writes to ISPENDR0 to set the state pending state of
an SGI, we fail to convey this to the HW if this SGI is already
backed by a GICv4.1 vSGI.

This is a bit of a corner case, as this would only occur if the
vgic state is changed on an already running VM, but this can
apparently happen across a guest reset driven by the VMM.

Fix this by always writing out the pending_latch value to the
HW, and reseting it to false.

Reported-by: Kunkun Jiang <jiangkunkun@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
Cc: stable@vger.kernel.org # 5.10+
Link: https://lore.kernel.org/r/7e7f2c0c-448b-10a9-8929-4b8f4f6e2a32@huawei.com