rt2x00: Add rt3390 support in rt2800 register initialization.

rt2x00: Add rt3390 support in rt2800 register initialization.

Add RT3390 specific register initializations to rt2x00, based on the latest
Ralink rt3390 vendor driver.

Untested as I don't actually own an RT3390 based device, but given experiences
on rt3070/rt3071 very hopeful that this will actually work..

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>