i40e: Fix dump output from debugfs calls

The debugfs commands that dump hex information are not doing these as
expected viz. "lldp get local", "nvm read", "dump debug fwdata", etc.

Use print_hex_dump() instead to hex dump and remove the print buffer
stuff from the code.

Change-Id: I507bd8b2187aae8bad5055b7872978c309cf143e
Signed-off-by: Neerav Parikh <Neerav.Parikh@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>