AHCI - Add conditional logic for wcache and rahead, enhanced reporting, fixes

AHCI - Add conditional logic for wcache and rahead, enhanced reporting, fixes

* Do not enable the write cache if the ident info says it is already enabled.

* Do not enable read-ahead if the ident info says it is already enabled.

* Do not try to set the freeze lock if the security feature is not supported.

* Enhanced error reporting.

* Report wcache and rahead state in the Ident.

NOTE: "WD My Book" ESATA consumer devices generate a fatal interface error
      when presented with ATA_C_SET_FEATURES.  The above code will quietly
      work around the problem.  The bug is likely in the My Book daughter
      board.