ssi: Add ssi_realize_and_unref()

ssi: Add ssi_realize_and_unref()

Add an ssi_realize_and_unref(), for the benefit of callers
who want to be able to create an SSI device, set QOM properties
on it, and then do the realize-and-unref afterwards.

The API works on the same principle as the recently added
qdev_realize_and_undef(), sysbus_realize_and_undef(), etc.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20200628142429.17111-9-peter.maydell@linaro.org