Fixes for several channel measurement facility bugs:
* Blocks copied from the hardware might not be consistent. Solve this
  by moving the copying into idle state and repeating the copying.
* avg_sample_interval changed with every read, even though no new block
  was available. Solve this by storing a timestamp when the last new
  block was received.
* Several locking issues.
* Measurements were not reenabled after a disconnected device became
  available again.
* Remove #defines for ioctls that were never implemented.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>