Get system state configuration from QEMU and patch DSDT with it.

Get system state configuration from QEMU and patch DSDT with it.

QEMU may want to disable guest's S3/S4 support and it wants to distinguish
between regular powerdown and S4 powerdown. To support that new fw_cfg
option was added that passes supported system states and what value should
guest use to enter each state. States are passed in 6 byte array. Each
byte represents one system state. If byte at offset X has its MSB set
it means that system state X is supported and to enter it guest should
use the value from lowest 7 bits. Patch also detects old QEMU and uses
values that work in backwards compatible way there.

Signed-off-by: Gleb Natapov <gleb@redhat.com>