KVM: arm: vgic-v2: Only use the virtual state when userspace accesses pending bits

There is no point in accessing the HW when writing to any of the
ISPENDR/ICPENDR registers from userspace, as only the guest should
be allowed to change the HW state.

Introduce new userspace-specific accessors that deal solely with
the virtual state. Note that the API differs from that of GICv3,
where userspace exclusively uses ISPENDR to set the state. Too
bad we can't reuse it.

Fixes: 82e40f55

 ("KVM: arm/arm64: vgic-v2: Handle SGI bits in GICD_I{S,C}PENDR0 as WI")
Reviewed-by: James Morse <james.morse@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>