lv_display_render_mode_t enum

Use the buffer(s) to render the screen is smaller parts. This way the buffers can be smaller then the display to save RAM. At least 1/10 screen size buffer(s) are recommended.

The buffer(s) has to be screen sized and LVGL will render into the correct location of the buffer. This way the buffer always contain the whole image. Only the changed ares will be updated. With 2 buffers the buffers' content are kept in sync automatically and in flush_cb only address change is required.

Always redraw the whole screen even if only one pixel has been changed. With 2 buffers in flush_cb only and address change is required.