Some work on the seek latency feature
- rewrite of the logical sector handling code to make seek latency support possible
- implemented variable HD seek latency for seek and read commands
- TODO #1: CD-ROM seek command returns status immediately, but it clears the DSC bit
  and sets it at completion. Device should not accept ATAPI commands until DSC is set.
- TODO #2: clean up the seek latency code


git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@12204 6c8e4198-a580-4521-a02f-c9ae86df1db9