wl1271: enable HW_AVAILABLE interrupt to fix ELP

We need to listen to HW_AVAILABLE interrupts when using ELP with firmware
revision 6.1.0.0.241.  Add WL1271_ACX_INTR_HW_AVAILABLE to the interrupts that
are enabled by default.

Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Reviewed-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>