ARM: socfpga: Description on FPGA bitstream type and file name for Arria 10

This patch adds description on properties about file name used for both
peripheral bitstream and core bitstream.

Signed-off-by: Tien Fong Chee <tien.fong.chee@intel.com>

doc/device-tree-bindings/fpga/altera-socfpga-a10-fpga-mgr.txt

@@ -7,8 +7,31 @@ Required properties:
                - The second index is for writing FPGA configuration data.
 - resets     : Phandle and reset specifier for the device's reset.
 - clocks     : Clocks used by the device.
+- altr,bitstream : Fit image file name for both FPGA peripheral bitstream,
+		   FPGA core bitstream and full bitstream.
 
-Example:
+		   Full bitstream, consist of peripheral bitstream and core
+		   bitstream.
+
+		   FPGA peripheral bitstream is used to initialize FPGA IOs,
+		   PLL, IO48 and DDR. This bitstream is required to get DDR up
+		   running.
+
+		   FPGA core bitstream contains FPGA design which is used to
+		   program FPGA CRAM and ERAM.
+
+Example: Bundles both peripheral bitstream and core bitstream into FIT image
+	 called fit_spl_fpga.itb. This FIT image can be created through running
+	 this command: tools/mkimage
+		       -E -p 400
+		       -f board/altera/arria10-socdk/fit_spl_fpga.its
+		       fit_spl_fpga.itb
+
+	 For details of describing structure and contents of the FIT image,
+	 please refer board/altera/arria10-socdk/fit_spl_fpga.its
+
+- Examples for booting with full release or booting with early IO release, then
+  follow by entering early user mode:
 
 	fpga_mgr: fpga-mgr@ffd03000 {
 		compatible = "altr,socfpga-a10-fpga-mgr";
@@ -16,4 +39,5 @@ Example:
 		       0xffcfe400 0x20>;
 		clocks = <&l4_mp_clk>;
 		resets = <&rst FPGAMGR_RESET>;
+		altr,bitstream = "fit_spl_fpga.itb";
 	};