Add clang-format file

Also run it across the whole tree to get everything using the One True Style.
We don't yet run this in an automated fashion as it's a little slow, but
there is a snippet to do so in makeall.sh.

Kernel/Devices/BlockDevice.h

@@ -10,7 +10,10 @@ public:
     virtual bool is_seekable() const override { return true; }
 
 protected:
-    BlockDevice(unsigned major, unsigned minor) : Device(major, minor) { }
+    BlockDevice(unsigned major, unsigned minor)
+        : Device(major, minor)
+    {
+    }
 
 private:
     virtual bool is_block_device() const final { return true; }