apm: fix shutdown

Qemu commit 9ee59f3 removed the bochs bios apm interface emulation at
port 0x8900.  That broke poweroff via APM.  Fix it by powering off the
machine using the acpi pm control register.

Old code is left in, so seabios wil try both poweroff methods.  Cleaning
that eventually up is left for another patch, after checking it isn't
needed.  Qemu never implemented "Standby" and "Suspend", only
"Shutdown", so it looks like there might be non-qemu use cases (bochs

Easiest way to test this is the syslinux poweroff module; modern linux
distros usually have CONFIG_APM turned off.

Reported-by: Sebastian Herbszt <herbszt@gmx.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit 5b63109242042372c1d6c3d23602e980f1c9637b)

4 files changed