hw/acpi/piix4: move PIIX4PMState into separate piix4.h header

This allows the QOM types in hw/acpi/piix4.c to be used elsewhere by simply including
hw/acpi/piix4.h.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220528091934.15520-5-mark.cave-ayland@ilande.co.uk>
Reviewed-by: Bernhard Beschow <shentey@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index 73d0bf5..cad6f5a 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -44,6 +44,7 @@
 #include "hw/acpi/tpm.h"
 #include "hw/acpi/vmgenid.h"
 #include "hw/acpi/erst.h"
+#include "hw/acpi/piix4.h"
 #include "sysemu/tpm_backend.h"
 #include "hw/rtc/mc146818rtc_regs.h"
 #include "migration/vmstate.h"