irqchip/gic-v3-its: Fix GICv4.1 VPE affinity update

When updating the affinity of a VPE, the VMOVP command is currently skipped
if the two CPUs are part of the same VPE affinity.

But this is wrong, as the doorbell corresponding to this VPE is still
delivered on the 'old' CPU, which screws up the balancing.  Furthermore,
offlining that 'old' CPU results in doorbell interrupts generated for this
VPE being discarded.

The harsh reality is that VMOVP cannot be elided when a set_affinity()
request occurs. It needs to be obeyed, and if an optimisation is to be
made, it is at the point where the affinity change request is made (such as
in KVM).

Drop the VMOVP elision altogether, and only use the vpe_table_mask
to try and stay within the same ITS affinity group if at all possible.

Fixes: dd3f050a (irqchip/gic-v4.1: Implement the v4.1 flavour of VMOVP)
Reported-by: Kunkun Jiang <jiangkunkun@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20240213101206.2137483-4-maz@kernel.org