radio: Remove unneeded buffer copy

memcpy should be avoided at all. Buffer address can be assigned directly
to NRF_RADIO->PACKETPTR register.

This way, provided buffers must be non-const because Radio's EastDMA
requires an address in the RAM.
radio: Remove unneeded radio_packet struct

Copy packets between layers should not be encouraged. Even using newlib
memcpy implementation, each memory copy of the radio packets can take
more than 10us.
ll: Remove unneeded type definition

Advertising PDUs will not be exposed to the upper/down layers, it will
be restricted to ll.c source file. Even if it was declared in a header
file typedef'd structs pollutes the global namespace and may cause
ordering relationships among header files.
ll: Remove unneeded static variable
ll: Change ADV_NONCONN_IND inter-PDU interval to 10ms
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: Disable busy checking
example: Add scannable advertising
WIP