ice: move debugfs code to fwlog

This code is only used in fwlog. Moved it there for easier lib creation.
There is a circular dependency between debugfs and fwlog. Moving to one
file is fixing it.

Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>