bnxt_en: Refactor bnxt_rdma_aux_device_init/uninit functions

In its current form, bnxt_rdma_aux_device_init() not only initializes
the necessary data structures of the newly created aux device but also
adds the aux device into the aux bus subsytem. Refactor the logic into
separate functions, first function to initialize the aux device along
with the required resources and second, to actually add the device to
the aux bus subsytem.
This separation helps to create bnxt_en_dev much earlier and save its
resources separately.

Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
Signed-off-by: Vikas Gupta <vikas.gupta@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20240409215431.41424-5-michael.chan@broadcom.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>