bng_en: Add devlink interface

bng_en: Add devlink interface

Allocate a base device and devlink interface with minimal
devlink ops.
Add dsn and board related information.
Map PCIe BAR (bar0), which helps to communicate with the
firmware.

Signed-off-by: Vikas Gupta <vikas.gupta@broadcom.com>
Reviewed-by: Bhargava Chenna Marreddy <bhargava.marreddy@broadcom.com>
Reviewed-by: Rajashekar Hudumula <rajashekar.hudumula@broadcom.com>
Link: https://patch.msgid.link/20250701143511.280702-3-vikas.gupta@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>