ide-tape: remove pipelined mode operation

Hi Bart,

here's the 1st draft of the pipeline removal series. As the diffstat below openly states it, a lot of code got removed - even more than the cleanup series we did earlier. There are several issues that we need to address concerning these patches:

1. only compile-tested since i don't have the hardware, i.e. longer -mm brewing is advisable the least.

2. I have left the tape->merge_stage buffer structure along with its alloc/free functions intact for now, for simplicity. The next step would be to go and carefully audit the code and then remove that last piece too and use allocations on the stack instead. I guess we still expect Jens's response on whether blk_{get,put}_request is the way to go here.

Jens?

3. After applying those we're moving into the direction of a lightweight ide-tape driver so the stanza for its removal in Documentation/feature-removal-schedule.txt becomes incorrect.

4. ... (i'm sure you're gonna have some more :))

 Documentation/ide/ide-tape.txt |  211 +++------
 drivers/ide/ide-tape.c         | 1032 +++-------------------------------------
 2 files changed, 134 insertions(+), 1109 deletions(-)