nrf/bluetooth: Improve advertisment behavior for nrf52 targets.

This patch makes sure that advertisment data is located in
persistent static RAM memory throughout the advertisment.

Also, setting m_adv_handle to predifined
BLE_GAP_ADV_SET_HANDLE_NOT_SET value to indicate first time
usage of the handle. Upon first advertisment configuration
this will be populated with a handle value returned by the
stack (s132/s140).