pds_fwctl: initial driver framework

Initial files for adding a new fwctl driver for the AMD/Pensando PDS
devices.  This sets up a simple auxiliary_bus driver that registers
with fwctl subsystem.  It expects that a pds_core device has set up
the auxiliary_device pds_core.fwctl

Link: https://patch.msgid.link/r/20250320194412.67983-5-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>