nrf51822/timer: Implement timer API using TIMER0
nrf51822/radio: Override BLE deviation parameters
radio: Add radio_driver

This patch adds a new radio event handler mechanism allowing to avoid
unneeded upper layer notifications, and group radio settings.
radio: Add RX option to radio_send()
radio: Add radio_reply() API
examples: Add scannable broadcaster
examples/radio-broadcaster: Remove duplicate timer initialization