e1000: allow user to disable ich8 lock loss workaround

The workaround for the ich8 lock loss problem is only needed for
a very small amount of systems. This adds an option for the user
to disable the workaround.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>