ICH9 LPC: handle GSI as qdev GPIO

The ICH9 LPC bridge has 24 output IRQs connected to GSI. Currently the IRQs are
referenced by pointers. The pointers are initialized at startup by direct access
to the structure fields. This violates Qemu device model.

The patch makes the IRQs handling to use GPIO model.

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