hw/acpi/piix4: rename piix4_pm_init() to piix4_pm_initfn()

hw/acpi/piix4: rename piix4_pm_init() to piix4_pm_initfn()

When QOMifying a device it is typical to use _init() as the suffix for an
instance_init function, however this name is already in use by the legacy
piix4_pm_init() wrapper function. Eventually the wrapper function will be
removed, but for now rename it to piix4_pm_initfn() to avoid a naming
collision.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220528091934.15520-7-mark.cave-ayland@ilande.co.uk>
Reviewed-by: Bernhard Beschow <shentey@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>