x86_64: generate a seed for the RNG with RDRAND when available

arch/x86_64/random.S

@@ -0,0 +1,43 @@
+.code64
+
+.global ml_hwrng_available
+.type ml_hwrng_available, @function
+
+ml_hwrng_available:
+	push %rbp
+	mov %rsp, %rbp
+	push %rbx
+	push %rdx
+
+	mov $1, %eax
+	mov $0, %ecx
+
+	cpuid
+
+	shr $30, %ecx
+	and $1, %ecx
+	mov %ecx, %eax
+
+	pop %rdx
+	pop %rbx
+	pop %rbp
+	ret
+
+.global ml_hwrng_generate
+.type ml_hwrng_generate, @function
+
+ml_hwrng_generate:
+	push %rbp
+	mov %rsp, %rbp
+
+	mov $100, %rcx
+.retry:
+	rdrand %rax
+	jc .done
+	loop .retry
+
+.fail:
+	mov $0, %rax
+.done:
+	pop %rbp
+	ret