So far the (legacy) IRQ line for a PCI device is allocated in devices.c,
which should actually not take care of that. Since we allocate all other
device specific resources in the actual device emulation code, the IRQ
should not be something special.

Remove the PCI specific code from devices.c, and move the IRQ line
allocation to the PCI code.
This drops the IRQ line from the VESA device, since it does not use one.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>