hw/acpi/ich9: Add periodic and swsmi timer

hw/acpi/ich9: Add periodic and swsmi timer

This patch implements the periodic and the swsmi ICH9 chipset timers. They are
especially useful when prototyping UEFI firmware (e.g. with EDK2's OVMF)
using QEMU.

For backwards compatibility, the compat properties "x-smi-swsmi-timer",
and "x-smi-periodic-timer" are introduced.

Additionally, writes to the SMI_STS register are enabled for the
corresponding two bits using a write mask to make future work easier.

Signed-off-by: Dominic Prinz <git@dprinz.de>
Message-Id: <1d90ea69e01ab71a0f2ced116801dc78e04f4448.1725991505.git.git@dprinz.de>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>