target-arm: Use MemoryListener to identify GIC base address for KVM

target-arm: Use MemoryListener to identify GIC base address for KVM

When using an in-kernel GIC with KVM, we need to tell the kernel where
the GIC's memory mapped registers live. Do this by registering a
MemoryListener which tracks where the board model maps the A15's
private peripherals, so we can finish the GIC initialisation
when the GIC is actually mapped.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>