IB/uverbs: Refactor uverbs_finalize_objects

uverbs_finalize_objects is currently used only to commit or abort
objects. Since we want to add automatic allocation/free of PTR_IN
attributes, moving it to uverbs_ioctl.c and renamit it to
uverbs_finalize_attrs.

Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>