cmd: fpga: Add support to load secure bitstreams

This patch adds support to load secure bitstreams(authenticated or
encrypted or both). As of now, this feature is added and tested only
for xilinx bitstreams and the secure bitstream was generated using
xilinx bootgen tool, but the command is defined in more generic way.

Command example to load authenticated and device key
encrypted bitstream is as follows
"fpga loads 0 100000 2000000 0 1"

Signed-off-by: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index d532c9f..c4e831e 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -697,6 +697,13 @@
 	  Supports loading an FPGA device from a bitstream buffer containing
 	  a partial bitstream.
 
+config CMD_FPGA_LOAD_SECURE
+	bool "fpga loads - loads secure bitstreams (Xilinx only)"
+	depends on CMD_FPGA
+	help
+	  Enables the fpga loads command which is used to load secure
+	  (authenticated or encrypted or both) bitstreams on to FPGA.
+
 config CMD_FPGAD
 	bool "fpgad - dump FPGA registers"
 	help