caif-hsi: Replace platform device with ops structure.

Remove use of struct platform_device, and replace it with
struct cfhsi_ops. Updated variable names in the same
spirit:
cfhsi_get_dev to cfhsi_get_ops,
cfhsi->dev to cfhsi->ops and,
cfhsi->dev.drv to cfhsi->ops->cb_ops.

Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>