wl12xx: add support for new WL1271 chip revision

This patch adds the code that recognizes the new WL1271 chip revision (PG 2.0).
Full support for this chip is not yet implemented and support for WL1271 PG 1.0
is not guaranteed anymore.

Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: Kalle Valo <kalle.valo@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>