pc: acpi-build: drop remaining ssdt_misc template

pc: acpi-build: drop remaining ssdt_misc template

It drops empty ssdt_misc templete. It also hides
from user almost all pointer arithmetic when building
SSDT which makes resulting code a bit cleaner
and concentrating only on composing ASL construct
/i.e. a task build_ssdt() should be doing/.

Also it makes one binary blob less stored in QEMU
source tree by removing need to keep and update
hw/i386/ssdt-misc.hex.generated file here in total
saving us ~430LOC.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>