IB/core: Initialize ib_device.dev.parent earlier

Move the ib_device.dev.parent initialization code from
ib_device_register_sysfs() to ib_register_device(). Additionally,
allow HBA drivers to set ib_device.dev.parent without setting
ib_device.dma_device. This is the first step towards removing
ib_device.dma_device.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>