kvm: rename kvm_irqchip_[add,remove]_irqfd_notifier with gsi suffix

Anticipating for the introduction of new add/remove functions taking
a qemu_irq parameter, let's rename existing ones with a gsi suffix.

Signed-off-by: Eric Auger <eric.auger@linaro.org>
Tested-by: Vikram Sethi <vikrams@codeaurora.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>