Kernel: Harvest randomness from various drivers

Random now gets entropy from the following drivers:
- KeyboardDevice
- PATAChannel
- PS2MouseDevice
- E1000NetworkAdapter
- RTL8139NetworkAdapter

Of these devices,  PS2MouseDevice and PATAChannel provide the vast
majority of the entropy.

Kernel/Devices/KeyboardDevice.cpp

@@ -287,6 +287,8 @@ void KeyboardDevice::handle_irq(const RegisterState&)
         u8 ch = raw & 0x7f;
         bool pressed = !(raw & 0x80);
 
+        m_entropy_source.add_random_event(raw);
+
         if (raw == 0xe0) {
             m_has_e0_prefix = true;
             return;