Kernel+LibC: Add a DebugLogDevice that forwards everything to I/O port 0xe9.

This is then used to implement the userspace dbgprintf() in a far more
efficient way than what we had before. :^)

Kernel/Devices/DebugLogDevice.cpp

@@ -0,0 +1,28 @@
+#include <Kernel/Devices/DebugLogDevice.h>
+#include <Kernel/IO.h>
+
+static DebugLogDevice* s_the;
+
+DebugLogDevice& DebugLogDevice::the()
+{
+    ASSERT(s_the);
+    return *s_the;
+}
+
+DebugLogDevice::DebugLogDevice()
+    : CharacterDevice(1, 18)
+{
+    s_the = this;
+}
+
+DebugLogDevice::~DebugLogDevice()
+{
+}
+
+ssize_t DebugLogDevice::write(Process&, const byte* data, ssize_t data_size)
+{
+    for (int i = 0; i < data_size; ++i)
+        IO::out8(0xe9, data[i]);
+    return data_size;
+}
+

Kernel/Devices/DebugLogDevice.h

@@ -0,0 +1,17 @@
+#include <Kernel/Devices/CharacterDevice.h>
+
+class DebugLogDevice final : public CharacterDevice {
+public:
+    DebugLogDevice();
+    virtual ~DebugLogDevice() override;
+
+    static DebugLogDevice& the();
+
+private:
+    // ^CharacterDevice
+    virtual ssize_t read(Process&, byte*, ssize_t) override { return 0; }
+    virtual ssize_t write(Process&, const byte*, ssize_t) override;
+    virtual bool can_write(Process&) const override { return true; }
+    virtual bool can_read(Process&) const override { return true; }
+    virtual const char* class_name() const override { return "DebugLogDevice"; }
+};