murdock: nordic_softdevice_ble: softdevice.hex is a test input
murdock: nordic_softdevice_ble: softdevice.hex is a test input

When running tests using 'nordic_softdevice_ble', the 'softdevice.hex'
file must also be taken into account for the test hashing and be
uploaded to the separated murdock testing boards.

When listed as dependency from `test-input-hash` the file must have a
target, which he has not. The file is implicitly created when compiling
`ELFFILE` so declare it as order only dependency.
In practice `BASELIBS` could be enough or even `pkg-build-softdevice`
but I do not want to be depend that much on internals there.

kaspar030/RIOT,ant9000/RIOT,toonst/RIOT,OTAkeys/RIOT,smlng/RIOT,josephnoir/RIOT,OTAkeys/RIOT,mtausig/RIOT,cladmi/RIOT,kaspar030/RIOT,toonst/RIOT,miri64/RIOT,aeneby/RIOT,x3ro/RIOT,kYc0o/RIOT,ant9000/RIOT,rfuentess/RIOT,kYc0o/RIOT,cladmi/RIOT,basilfx/RIOT,yogo1212/RIOT,authmillenon/RIOT,smlng/RIOT,basilfx/RIOT,basilfx/RIOT,OlegHahm/RIOT,yogo1212/RIOT,toonst/RIOT,josephnoir/RIOT,OTAkeys/RIOT,mtausig/RIOT,cladmi/RIOT,yogo1212/RIOT,ant9000/RIOT,jasonatran/RIOT,jasonatran/RIOT,cladmi/RIOT,aeneby/RIOT,aeneby/RIOT,josephnoir/RIOT,kaspar030/RIOT,josephnoir/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,mtausig/RIOT,ant9000/RIOT,OlegHahm/RIOT,toonst/RIOT,ant9000/RIOT,x3ro/RIOT,basilfx/RIOT,rfuentess/RIOT,cladmi/RIOT,smlng/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,smlng/RIOT,josephnoir/RIOT,authmillenon/RIOT,toonst/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,authmillenon/RIOT,miri64/RIOT,OlegHahm/RIOT,mtausig/RIOT,kYc0o/RIOT,miri64/RIOT,authmillenon/RIOT,aeneby/RIOT,kaspar030/RIOT,kaspar030/RIOT,kYc0o/RIOT,authmillenon/RIOT,yogo1212/RIOT,yogo1212/RIOT,mtausig/RIOT,miri64/RIOT,OlegHahm/RIOT,smlng/RIOT,kYc0o/RIOT,rfuentess/RIOT,rfuentess/RIOT,yogo1212/RIOT,rfuentess/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,basilfx/RIOT,RIOT-OS/RIOT,x3ro/RIOT,x3ro/RIOT,OlegHahm/RIOT,miri64/RIOT,x3ro/RIOT,aeneby/RIOT,jasonatran/RIOT,jasonatran/RIOT