Kernel: Move devices into Kernel/Devices/.

Kernel/Devices/BlockDevice.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <Kernel/Devices/Device.h>
+
+class BlockDevice : public Device {
+public:
+    virtual ~BlockDevice() override;
+
+    virtual Region* mmap(Process&, LinearAddress preferred_laddr, size_t offset, size_t size) = 0;
+
+protected:
+    BlockDevice(unsigned major, unsigned minor) : Device(major, minor) { }
+
+private:
+    virtual bool is_block_device() const final { return true; }
+};