hw/smbios: add options for type 4 max-speed and current-speed

hw/smbios: add options for type 4 max-speed and current-speed

Common VM users sometimes care about CPU speed, so we add two new
options to allow VM vendors to present CPU speed to their users.
Normally these information can be fetched from host smbios.

Strictly speaking, the "max speed" and "current speed" in type 4
are not really for the max speed and current speed of processor, for
"max speed" identifies a capability of the system, and "current speed"
identifies the processor's speed at boot (see smbios spec), but some
applications do not tell the differences.

Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Ying Fang <fangying1@huawei.com>
Signed-off-by: Heyi Guo <guoheyi@huawei.com>
Message-Id: <20200806035634.376-2-fangying1@huawei.com>