net: bnge: add AUXILIARY_BUS to Kconfig dependencies

net: bnge: add AUXILIARY_BUS to Kconfig dependencies

The build can currently fail with

    ld: drivers/net/ethernet/broadcom/bnge/bnge_auxr.o: in function `bnge_rdma_aux_device_add':
    bnge_auxr.c:(.text+0x366): undefined reference to `__auxiliary_device_add'
    ld: drivers/net/ethernet/broadcom/bnge/bnge_auxr.o: in function `bnge_rdma_aux_device_init':
    bnge_auxr.c:(.text+0x43c): undefined reference to `auxiliary_device_init'

if BNGE is enabled but no other driver pulls in AUXILIARY_BUS.

Select AUXILIARY_BUS in BNGE like in all other drivers which create
an auxiliary_device.

Fixes: 8ac050ec3b1c ("bng_en: Add RoCE aux device support")
Signed-off-by: Markus Blöchl <markus@blochl.de>
Reviewed-by: Vikas Gupta <vikas.gupta@broadcom.com>
Link: https://patch.msgid.link/20251228-bnge_aux_bus-v1-1-82e273ebfdac@blochl.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>