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 <jsnow@redhat.com>
Cc: qemu-block@nongnu.org
Cc: Rob Herring <robh@kernel.org>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Alistair Francis <alistair.francis@xilinx.com>
Cc: "Edgar E. Iglesias" <edgar.iglesias@gmail.com>
Cc: Marcel Apfelbaum <marcel@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Acked-by: John Snow <jsnow@redhat.com>
Acked-by: Marcel Apfelbaum <marcel@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170503203604.31462-11-ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>