bng_en: Add a network device

bng_en: Add a network device

Add a network device with netdev features enabled.
Some features are enabled based on the capabilities
advertised by the firmware. Add the skeleton of minimal
netdev operations. Additionally, initialize the parameters
for rings (TX/RX/Completion).

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/20250701143511.280702-11-vikas.gupta@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>