ice: rename devlink_port.[ch] to port.[ch]

Drop "devlink_" prefix from files that sit in devlink/.
I'm going to add more files there, and repeating "devlink" does not feel
good. This is also the scheme used in most other places, most notably the
devlink core files are named like that.

devlink.[ch] stays as is.

Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>