fpga: add option for loading FPGA secure bitstreams

fpga: add option for loading FPGA secure bitstreams

It allows using this feature without enabling the "fpga loads"
command.

Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>
Co-developed-by: Adrian Fiergolski <adrian.fiergolski@fastree3d.com>
Signed-off-by: Adrian Fiergolski <adrian.fiergolski@fastree3d.com>
Tested-by: Ricardo Salveti <ricardo@foundries.io>
Tested-by: Adrian Fiergolski <adrian.fiergolski@fastree3d.com>
Link: https://lore.kernel.org/r/20220722141614.297383-2-oleksandr.suvorov@foundries.io
Signed-off-by: Michal Simek <michal.simek@amd.com>