ixgbe: collect all 82599 AUTOC code in one function

When reading or writing to the AUTOC register on 82599 devices we need to
preform various operations that aren't needed for other MAC types.  This
patch will collect all of that code into one place to minimize MAC checks
in common code paths.

While doing this I also clean up some cases where we weren't holding the
SW/FW semaphore during a read/modify/write of AUTOC.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>