IB/core: Store default GID property per-table instead of per-entry

There are at max one or two default GIDs for RoCE. Instead of storing
a default GID property for all the GIDs, store default GID indices as
individual bit per table.

This allows a future simplification to get rid of the GID property field.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>