rt2x00: Finish rt3070 support in rt2800 register initialization.

rt2x00 had preliminary support for RT3070 based devices, but the support was
incomplete.
Update the RT3070 register initialization to be similar to the latest Ralink
vendor driver.

With this patch my rt3070 based devices start showing a sign of life.

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>