cmd: pxe_utils: sysboot: add kaslr-seed generation support

this will add kaslrseed keyword to sysboot lable,
when it set, it will request to genarate random number
from hwrng as kaslr-seed.

with this patch exlinux.conf label looks like

label l0
        menu testing
        linux /boot/vmlinuz-5.15.16-arm
        initrd /boot/initramfs-5.15.16-arm.img
        fdtdir /boot/dtbs/5.15.16-arm/
        kaslrseed
        append root=UUID=92ae1e50-eeeb-4c5b-8939-7e1cd6cfb059 ro

Tested on Khadas VIM with kernel 5.16.0-rc5-arm64, Debian 11.

Signed-off-by: Zhang Ning <zhangn1985@qq.com>
diff --git a/include/pxe_utils.h b/include/pxe_utils.h
index dad2668..4a73b2a 100644
--- a/include/pxe_utils.h
+++ b/include/pxe_utils.h
@@ -33,6 +33,7 @@
  * initrd - path to the initrd to use for this label.
  * attempted - 0 if we haven't tried to boot this label, 1 if we have.
  * localboot - 1 if this label specified 'localboot', 0 otherwise.
+ * kaslrseed - 1 if generate kaslrseed from hw_rng
  * list - lets these form a list, which a pxe_menu struct will hold.
  */
 struct pxe_label {
@@ -50,6 +51,7 @@
 	int attempted;
 	int localboot;
 	int localboot_val;
+	int kaslrseed;
 	struct list_head list;
 };