Kernel: Set up an initial boot framebuffer console

Instead of seeing a black screen until GraphicsManagement was fully
initialized, this allows us to see the console output much earlier.
So, if the bootloader provided us with a framebuffer, set up a console
as early as possible.

Kernel/Graphics/Console/BootFramebufferConsole.h

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2022, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <Kernel/Forward.h>
+#include <Kernel/Graphics/Console/GenericFramebufferConsole.h>
+
+namespace Kernel::Graphics {
+
+class BootFramebufferConsole : public GenericFramebufferConsoleImpl {
+public:
+    virtual void clear(size_t x, size_t y, size_t length) override;
+    virtual void write(size_t x, size_t y, char ch, Color background, Color foreground, bool critical = false) override;
+    using GenericFramebufferConsoleImpl::write;
+
+    virtual void enable() override;
+    virtual void disable() override;
+
+    virtual void flush(size_t, size_t, size_t, size_t) override { }
+    virtual void set_resolution(size_t, size_t, size_t) override { }
+
+    BootFramebufferConsole(PhysicalAddress framebuffer_addr, size_t width, size_t height, size_t pitch);
+
+protected:
+    virtual void clear_glyph(size_t x, size_t y) override;
+
+    virtual u8* framebuffer_data() override;
+
+    OwnPtr<Memory::Region> m_framebuffer;
+    u8* m_framebuffer_data {};
+    mutable Spinlock m_lock;
+};
+
+}