KVM: arm/arm64: GICv4: Unmap VLPI when freeing an LPI

When freeing an LPI (on a DISCARD command, for example), we need
to unmap the VLPI down to the physical ITS level.

Acked-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>