IB/hfi1: Hold i2c resource across debugfs open/close

External i2c firmware updates are done in multiple steps and
cannot have other things done in between.  For debugfs files,
acquire the resource on open and release it on close.

Reviewed-by: Mitko Haralanov <mitko.haralanov@intel.com>
Reviewed-by: Easwar Hariharan <easwar.hariharan@intel.com>
Signed-off-by: Dean Luick <dean.luick@intel.com>
Signed-off-by: Jubin John <jubin.john@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>