S110 compatibility is already present, but this patch adds proper handling
of observer/central related features:
* Gap::startScan will return BLE_ERRROR_NOT_IMPLEMENTED (instead of
PARAM_OUT_OF_RANGE)
* nRF5xGattClient uses the default GattClient implementation when S110 is
in use. All if its methods return NOT_IMPLEMENTED.
Example: for an application that acts as both a central and a peripheral,
using S110 will make the ble.gap().startScan() call return
BLE_ERROR_NOT_IMPLEMENTED, and advertisement features will continue
running normally.
In addition, with GCC, this patch will free 344 bytes of RAM and 2504
bytes of flash.