Kernel: Commit the profiling sample buffer memory up front

This avoids getting page faults while storing samples in the timer IRQ.

Kernel/Profiling.cpp

@@ -48,6 +48,7 @@ void start(Process& process)
 
     if (!s_profiling_buffer) {
         s_profiling_buffer = RefPtr<KBufferImpl>(KBuffer::create_with_size(8 * MB).impl()).leak_ref();
+        s_profiling_buffer->region().commit();
         s_slot_count = s_profiling_buffer->size() / sizeof(Sample);
     }