hw/i386/vmport: Add support for CMD_GETBIOSUUID

hw/i386/vmport: Add support for CMD_GETBIOSUUID

This is VMware documented functionallity that some guests rely on.
Returns the BIOS UUID of the current virtual machine.

Note that we also introduce a new compatability flag "x-cmds-v2" to
make sure to expose new VMPort commands only to new machine-types.
This flag will also be used by the following patches that will introduce
additional VMPort commands.

Reviewed-by: Nikita Leshenko <[email protected]>
Signed-off-by: Liran Alon <[email protected]>
Message-Id: <20200312165431[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>