arm: sve_addvl test program that prints sve length

userland/arch/aarch64/inline_asm/sve_addvl.c

@@ -0,0 +1,15 @@
+/* https://cirosantilli.com/linux-kernel-module-cheat#arm-sve-vaddl-instruction */
+
+#include <inttypes.h>
+#include <stdio.h>
+
+int main(void) {
+    uint64_t vl = 0;
+    __asm__ (
+        "addvl %[vl], %[vl], #8"
+        : [vl] "+r" (vl)
+        :
+        :
+    );
+    printf("0x%" PRIX64 "\n", vl);
+}