RDMA/core: Clean up cq pool mechanism

RDMA/core: Clean up cq pool mechanism

The CQ pool mechanism had two problems:

1. The CQ pool lists were uninitialized in the device registration error
   flow.  As a result, all the list pointers remained NULL.  This caused
   the kernel to crash (in procedure ib_cq_pool_destroy) when that error
   flow was taken (and unregister called).  The stack trace snippet:

     BUG: kernel NULL pointer dereference, address: 0000000000000000
     #PF: supervisor read access in kernel mode
     #PF: error_code(0×0000) ? not-present page
     PGD 0 P4D 0
     Oops: 0000 [#1] SMP PTI
     . . .
     RIP: 0010:ib_cq_pool_destroy+0x1b/0×70 [ib_core]
     . . .
     Call Trace:
      disable_device+0x9f/0×130 [ib_core]
      __ib_unregister_device+0x35/0×90 [ib_core]
      ib_register_device+0x529/0×610 [ib_core]
      __mlx5_ib_add+0x3a/0×70 [mlx5_ib]
      mlx5_add_device+0x87/0×1c0 [mlx5_core]
      mlx5_register_interface+0x74/0xc0 [mlx5_core]
      do_one_initcall+0x4b/0×1f4
      do_init_module+0x5a/0×223
      load_module+0x1938/0×1d40

2. At device unregister, when cleaning up the cq pool, the cq's in the
   pool lists were freed, but the cq entries were left in the list.

The fix for the first issue is to initialize the cq pool lists when the
ib_device structure is allocated for a new device (in procedure
_ib_alloc_device).

The fix for the second problem is to delete cq entries from the pool lists
when cleaning up the cq pool.

In addition, procedure ib_cq_pool_destroy() is renamed to the more
appropriate name ib_cq_pool_cleanup().

Fixes: 4aa1615268a8 ("RDMA/core: Fix ordering of CQ pool destruction")
Link: https://lore.kernel.org/r/20201208073545.9723-2-leon@kernel.org
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>