fwctl/bnxt_fwctl: Add bnxt fwctl device

fwctl/bnxt_fwctl: Add bnxt fwctl device

Create bnxt_fwctl device. This will bind to bnxt's aux device.
On the upper edge, it will register with the fwctl subsystem.
It will make use of bnxt's ULP functions to send FW commands.

Link: https://patch.msgid.link/r/20260314151605.932749-5-pavan.chebbi@broadcom.com
Reviewed-by: Andy Gospodarek <gospo@broadcom.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>