Getting rid of the repeated code in the driver when deciding on the page
size of the hardware ring memory. A new common function would translate
the ring page size into device specific page size.

Link: https://lore.kernel.org/r/1585851136-2316-2-git-send-email-devesh.sharma@broadcom.comSigned-off-by: Devesh Sharma <devesh.sharma@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>