fpga: stratix10-soc: make FPGA task un-interruptible

When CTRL+C occurs during the process of FPGA reconfiguration, the FPGA
reconfiguration process stops and the user can't perform a new FPGA
reconfiguration properly.

Set FPGA task to be not interruptible so that the user can properly
perform FPGA reconfiguration after CTRL+C event.

Signed-off-by: Richard Gong <richard.gong@intel.com>
Reviewed-by: Tom Rix <trix@redhat.com>
Signed-off-by: Moritz Fischer <mdf@kernel.org>