rt2x00: add queue_init callback to rt2x00_ops

The driver uses static data structures for initializing
specific fields of a given data queue. These static
queue data descriptor structures are containing values
which related to a given chipset.

Even though the values are chip specific, the actual
selection of the used structure is based on device
specific vendor/product identifiers. This approach works,
but it is not always reliable. Sometimes the vendor and/or
device IDs of the PCI and USB devices contains improper
values which makes it impossible to select the correct
structure for such devices.

The patch adds a new callback to tr2x00_ops which
is called after the chipset detection is finished.
This allows the drivers to do dynamic initialization
of the data_queue structure for a given queue based
on the actual chipset.

After each driver implements the queue_init callback,
the data_queue_desc structure will be removed.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Acked-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>