sdl: Keep texture around, upload LCD-parts only

No need to create a new texture for every
rendered frame, unless the scaling method
has been adjusted.

We also don't need to upload the (unchanged)
player interface to GPU memory repeatedly.

+ Remove unused lcd_display_redraw &
having_new_lcd variables

Change-Id: I5bff6aa2d54347a3f2c3afba8d8d7eb9e39f77f7

firmware/target/hosted/sdl/lcd-sdl.h

@@ -25,15 +25,6 @@
 #include "lcd.h"
 #include "SDL.h"
 
-/* Default display zoom level */
-extern SDL_Surface *gui_surface;
-extern SDL_Renderer *sdlRenderer;
-extern SDL_Window *window;
-
-void sdl_get_window_dimensions(int *w, int *h);
-int sdl_update_window(void);
-void sdl_window_needs_update(void);
-
 void sdl_update_rect(SDL_Surface *surface, int x_start, int y_start, int width,
                      int height, int max_x, int max_y,
                      unsigned long (*getpixel)(int, int));