wl1251: Add IRQ looping support

Add support for IRQ looping. Helps in the case that we have e.g. multiple
packets coming from the network when we wake up from the ELP.

Signed-off-by: Janne Ylalehto <janne.ylalehto@nokia.com>
Reviewed-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
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>