sysbus-ahci: Remove user_creatable flag

sysbus-ahci: Remove user_creatable flag

The sysbus-ahci devices are supposed to be created and wired by
code from other devices, like calxeda_init() and
xlnx_zynqmp_realize(), and won't work with -device. Remove the
user_creatable flag from the device class.

Cc: John Snow <[email protected]>
Cc: [email protected]
Cc: Rob Herring <[email protected]>
Cc: Peter Maydell <[email protected]>
Cc: Alistair Francis <[email protected]>
Cc: "Edgar E. Iglesias" <[email protected]>
Cc: Marcel Apfelbaum <[email protected]>
Reviewed-by: Alistair Francis <[email protected]>
Acked-by: John Snow <[email protected]>
Acked-by: Marcel Apfelbaum <[email protected]>
Signed-off-by: Eduardo Habkost <[email protected]>
Message-Id: <20170503203604[email protected]>
Signed-off-by: Eduardo Habkost <[email protected]>