mlx5ib: Limit mkey page size to 2GB

The maximum page size in the mkey context is 2GB.

Until today, we didn't enforce this requirement in the code, and therefore,
if we got a page size larger than 2GB, we have passed zeros in the
log_page_shift instead of the actual value and the registration failed.

This patch limits the driver to use compound pages of 2GB for mkeys.

Linux commit:
762f899ae7875554284af92b821be8c083227092

MFC after: 1 week
Reviewed by: kib
Sponsored by: Mellanox Technologies // NVIDIA Networking