ICH9 LPC: move call of isa_bus_irqs to 'realize' method

The isa_bus_irqs function initializes ISA bus IRQ array pointer with specified
value.

Previously the ICH9 LPC bridge model did not have its own IRQs but
only IRQ pointer cache. And same GSI were used for ISA bus and other sources
behind the bridge (PCI, SCI). Hence, the pc_q35_init was only possible place to
setup both ISA bus IRQs and the bridge IRQ cache.

As a result, the call of isa_bus_irqs was made from pc_q35_init.

Now the ICH9 LPC bridge has its own output IRQs which are connected to GSI. The
output IRQs are already used to route IRQs from PCI and SCI.

The patch makes the ICH9 LPC bridge output IRQs to used for ISA bus too.

Signed-off-by: Efimov Vasily <real@ispras.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
