hw/intc/s390_flic: Fix interrupt controller migration on s390x with TCG

hw/intc/s390_flic: Fix interrupt controller migration on s390x with TCG

Migration of a s390x guest with TCG was long known to be very unstable,
so the tests in tests/qtest/migration-test.c are disabled if running
with TCG instead of KVM.

Nicholas Piggin did a great analysis of the problem:

"The flic pending state is not migrated, so if the machine is migrated
 while an interrupt is pending, it can be lost. This shows up in
 qtest migration test, an extint is pending (due to console writes?)
 and the CPU waits via s390_cpu_set_psw and expects the interrupt to
 wake it. However when the flic pending state is lost, s390_cpu_has_int
 returns false, so s390_cpu_exec_interrupt falls through to halting
 again."

Thus let's finally migrate the pending state, and to be on the safe
side, also the other state variables of the QEMUS390FLICState structure.

Message-ID: <20240619144421.261342-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>