IB/core: Refactor idr to be per uverbs_file

The current code creates an idr per type. Since types are currently
common for all drivers and known in advance, this was good enough.
However, the proposed ioctl based infrastructure allows each driver
to declare only some of the common types and declare its own specific
types.

Thus, we decided to implement idr to be per uverbs_file.

Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Haggai Eran <haggaie@mellanox.com>
Reviewed-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>