cmd: kaslrseed: add command to generate value from hwrng

Allow the kaslr-seed value in the chosen node to be set from a hardware
rng source.

Tested on a Rockchip PX30 (Odroid Go Advance), you must have loaded
the devicetree first and prepared it for editing. On my device the
workflow goes as follows:

setenv dtb_loadaddr "0x01f00000"
load mmc 0:1 ${dtb_loadaddr} rk3326-odroid-go2.dtb
fdt addr ${dtb_loadaddr}
fdt resize
kaslrseed

and the output can be seen here:
fdt print /chosen
chosen {
        kaslr-seed = <0x6f61df74 0x6f7b996c>;
        stdout-path = "serial2:115200n8";
};

Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 5b30b13..02c298f 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1814,6 +1814,13 @@
 	help
 	  Print bytes from the hardware random number generator.
 
+config CMD_KASLRSEED
+	bool "kaslrseed"
+	depends on DM_RNG
+	help
+	  Set the kaslr-seed in the chosen node with entropy provided by a
+	  hardware random number generator.
+
 config CMD_SLEEP
 	bool "sleep"
 	default y