nikon: add 12bit entries if not present for all 14-bit
nikon: add 12bit entries if not present for all 14-bit

For all nikon cameras with 14-bit entries and no 12-bit entries,
add 12-bit entries with obviously-wrong white level,
and  supported="no".

This way the users will not recieve garbled images, and once
they provide a sample, the support can be easily added by
setting appropriate whitelevel and removing supported="no"

klauspost/rawspeed,anarsoul/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,klauspost/rawspeed,anarsoul/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,anarsoul/rawspeed,darktable-org/rawspeed