Avoids the need to have per IRQ a thread that blocks synchronously for next
interrupt. Now a thread may wait for multiple IRQs as other signals
simultaneously.
In core no threads are required anymore for IRQs/MSI - the clients (either
the pci_drv or in case of MSI the driver) gets the IRQ delivered directly as
a ordinary Genode signal.
Useful since #1216 and #1487 is now available.
Commit applies feature of #1446 also to IRQ/MSIs.
3e90542559