Kernel: Make Random work on CPUs without rdrand

- If rdseed is not available, fallback to rdrand.
- If rdrand is not available, block for entropy, or use insecure prng
  depending on if user wants fast or good random.

Kernel/init.cpp

@@ -131,7 +131,7 @@ extern "C" [[noreturn]] void init()
 
     klog() << "Starting SerenityOS...";
 
-    __stack_chk_guard = get_good_random<u32>();
+    __stack_chk_guard = get_fast_random<u32>();
 
     TimeManagement::initialize();
 
@@ -169,7 +169,7 @@ extern "C" [[noreturn]] void init()
 extern "C" [[noreturn]] void init_ap(u32 cpu)
 {
     APIC::the().enable(cpu);
-    
+
 #if 0
     Scheduler::idle_loop();
 #else