Clean up the driver
Clean up the driver

Move mac_timer_init() into set_poll_mode() and remove now unneccesary clear outs and mask outs of interrupt sources and pending interrupts
arurke/contiki,MohamedSeliem/contiki,arurke/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,arurke/contiki,arurke/contiki,arurke/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,arurke/contiki,arurke/contiki,MohamedSeliem/contiki