openssd: switch to dummy FTL

greedy FTL doesn't have support for ftl_trim.i Change to dummy which
have the stub implementation.
openssd: add support for lightnvm identify

For a disk to be detected as a LightNVM device, we set the second bit in
ithe DATA SET MANAGEMENT word to 1.
openssd: add lightnvm FTL stub files

Copied over from tutorial
openssd: add stubs for erase command
openssd: add support for lightnvm ata commands
add git ignore file for common files