lightnvm: no need for hash table in nvm_addr

Previous implementation needed this. We removed the usecase for it, lets
also remove it from the nvm_addr struct.
lightnvm: add nvme addr cache

To handle inflight data, where a page is being updated continuously, the
global translation map might change block and addr. Instead hand out
local copies of where the specific mapping is being used.

This implements a cache of addrs to be used for inflight IOs.