igb: Convert printks to pr_<level>

Based on original patch from Joe Perches <joe@perches.com>

Use the current logging styles.

pr_<level> conversions are now prefixed with "igb: "

Correct a defect where the trailing NTU may have been printed
on a separate line because of an interleaving hex_dump.

Remove unnecessary uses of KERN_CONT and use single pr_info()s
to avoid any possible output interleaving from other modules.

Coalesce formats as appropriate.

-v2 fix-up to make checkpatch.pl compliant and remove change to
    the copyright line

CC: Joe Perches <joe@perches.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>