bng_en: Add ring memory allocation support

bng_en: Add ring memory allocation support

Add ring allocation/free mechanism which help
to allocate rings (TX/RX/Completion) and backing
stores memory on the host for the device.
Future patches will use these functions.

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/20250701143511.280702-6-vikas.gupta@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>