rt2x00: Reorganize RT chipset setting for PCI/SOC devices.

Don't set the RT chipset for a device from within the generic PCI/SOC code,
but rather from the individual drivers, so that individual drivers have
more control over what RT chipset is set.
Preparation for chip handling updates for rt2800 devices.

Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>