hw/block: Fix pin-based interrupt behaviour of NVMe

Pin-based interrupt of NVMe controller did not work properly
because using an obsolated function pci_irq_pulse().
To fix this, change to use pci_irq_assert() / pci_irq_deassert()
instead of pci_irq_pulse().

Signed-off-by: Hikaru Nishida <hikarupsp@gmail.com>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>