pds_core: add new fwctl auxiliary_device

Add support for a new fwctl-based auxiliary_device for creating a
channel for fwctl support into the AMD/Pensando DSC.

Link: https://patch.msgid.link/r/20250320194412.67983-4-shannon.nelson@amd.com


Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>