Data TAG support

Meta:
Headline : Implement data tag feature in the Linux MMC layer - ext4 part
Acceptance: Accepted upstream by Ted Tso
Roadmap id: KWG2011-EMMC-4.5-SUPPORT

[jakub-pavelek 2012-11-09] Marked as Blocked as no-one is working on it. Candidate for removal.
[jakub-pavelek 2012-11-09] Unblocked, moving to Balaji T K, re-scoping a bit
[jakub-pavelek 2013-01-02] Blocked, no developer. Can go deferred if not resolved
[jakub-pavelek 2013-02-06] Un-blocking. Baali is back, LuPo wants to give helping hand. Moving to 3.10 though.
[jakub-pavelek 2013-02-26] Nothing was done during 13.02
[jakub-pavelek 2013-03-25] Nothing was done during 13.03. Balaji TK dropped off the radar. Moving to Backlog, no estimate on completion.

Work items for 12.01:
[saugata.das] Study data tag feature of MMC-4.5 : DONE
[saugata.das] Implement data tag feature : DONE
[saugata.das] Internal review, push to community : DONE
[saugata.das] Update mmci driver to handle SBC : DONE

Work items for 12.02:
[saugata.das] Study EXT4 for improving REQ_META usage : DONE
[saugata.das] Implement EXT4 changes for REQ_META : DONE
[saugata.das] Internal review : DONE
[saugata.das] Publish to EXT4 and FSDEVEL community : DONE

Work items for backlog:
[balajik] Rebase on top on 3.7: TODO
[balajik] Internal review : TODO
[balajik] Publish to EXT4 and FSDEVEL community : TODO