octeontx2-pf: Vary completion queue event size

Completion Queue Entry(CQE) is a descriptor written
by hardware to notify software about the send and
receive completion status. The CQE can be of size
128 or 512 bytes. A 512 bytes CQE can hold more receive
fragments pointers compared to 128 bytes CQE. This
patch enables to modify CQE size using:
<ethtool -G cqe-size N>.

Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>