Add a flag that is passed to the write_init() callback, indicating
that the bitstream is encrypted.

The low-level driver will deal with the flag, or return an error,
if encrypted bitstreams are not supported.
Signed-off-by: NMoritz Fischer <mdf@kernel.org>
Acked-by: NMichal Simek <michal.simek@xilinx.com>
Signed-off-by: NAlan Tull <atull@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>