fpga: Guard the LOADMK functionality with CMD_FPGA_LOADMK

Guard the LOADMK functionality with config to provide
an option to enable or disable it.
Enable it for all platforms in mainline which enable CONFIG_CMD_FPGA.

Signed-off-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/include/configs/iocon.h b/include/configs/iocon.h
index b32095c..79c4736 100644
--- a/include/configs/iocon.h
+++ b/include/configs/iocon.h
@@ -63,6 +63,7 @@
  */
 #define CONFIG_CMD_CACHE
 #define CONFIG_CMD_FPGA
+#define CONFIG_CMD_FPGA_LOADMK
 #undef CONFIG_CMD_EEPROM
 
 /*