Kernel: Implement fast scrolling for TTY

kernel/include/kernel/Device/FramebufferDevice.h

@@ -17,6 +17,10 @@ namespace Kernel
 
 		void set_pixel(uint32_t x, uint32_t y, uint32_t rgb);
 
+		// positive rows -> empty pixels on bottom
+		// negative rows -> empty pixels on top
+		void scroll(int32_t rows, uint32_t rgb);
+
 		void sync_pixels_full();
 		void sync_pixels_linear(uint32_t first_pixel, uint32_t pixel_count);
 		void sync_pixels_rectangle(uint32_t top_right_x, uint32_t top_right_y, uint32_t width, uint32_t height);

kernel/include/kernel/Terminal/FramebufferTerminal.h

@@ -15,6 +15,7 @@ namespace Kernel
 		virtual uint32_t height() const override { return m_framebuffer_device->height() / font().height(); }
 
 		virtual void putchar_at(uint16_t, uint32_t, uint32_t, Color, Color) override;
+		virtual bool scroll(Color) override;
 		virtual void clear(Color) override;
 
 		virtual void set_cursor_position(uint32_t, uint32_t) override;

kernel/include/kernel/Terminal/TerminalDriver.h

@@ -31,6 +31,7 @@ namespace Kernel
 		virtual uint32_t height() const = 0;
 
 		virtual void putchar_at(uint16_t, uint32_t, uint32_t, Color, Color) = 0;
+		virtual bool scroll(Color) { return false; }
 		virtual void clear(Color) = 0;
 
 		virtual void set_cursor_position(uint32_t, uint32_t) = 0;