bng_en: Add RoCE aux device support

bng_en: Add RoCE aux device support

Add an auxiliary (aux) device to support RoCE. The base driver is
responsible for creating the auxiliary device and allocating the
required resources to it, which will be owned by the bnge RoCE
driver in future patches.

Signed-off-by: Vikas Gupta <vikas.gupta@broadcom.com>
Link: https://patch.msgid.link/20251117171136.128193-2-siva.kallam@broadcom.com
Reviewed-by: Siva Reddy Kallam <siva.kallam@broadcom.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Leon Romanovsky <leon@kernel.org>