hw/ppc/prep: Fix wiring of PIC -> CPU interrupt

hw/ppc/prep: Fix wiring of PIC -> CPU interrupt

Commit cef2e7148e32 ("hw/isa/i82378: Remove intermediate IRQ forwarder")
passes s->cpu_intr to i8259_init() in i82378_realize() directly. However, s-
>cpu_intr isn't initialized yet since that happens after the south bridge's
pci_realize_and_unref() in board code. Fix this by initializing s->cpu_intr
before realizing the south bridge.

Fixes: cef2e7148e32 ("hw/isa/i82378: Remove intermediate IRQ forwarder")
Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20230304114043.121024-4-shentey@gmail.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
(cherry picked from commit 2237af5e60ada06d90bf714e85523deafd936b9b)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>