bnxt_en: Refactor bnxt_dl_register()

Define bnxt_dl_params_register() and bnxt_dl_params_unregister()
functions and move params register/unregister code to these newly
defined functions. This patch is in preparation to register
devlink irrespective of firmware spec. version in the next patch.

Signed-off-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>