cxgb3 - Expose HW memory page info

A HW issue requires limiting the receive window size
to 23 pages of internal memory.
These pages can be configured to different sizes,
thus the RDMA driver needs to know the
page size to enforce the upper limit.

Also assign explicit enum values.

Signed-off-by: Divy Le Ray <divy@chelsio.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>