debug: Report if double-buffered fb is enabled

(Only applies to hosted targets if FB_DOUBLEBUF is enabled)

Change-Id: I6ef3ead5f6ef12b26e3dd0d07ac582cff98deaed

firmware/export/lcd.h

@@ -657,4 +657,8 @@ extern void lcd_nine_segment_bmp(const struct bitmap* bm, int x, int y,
     extern int lcd_get_dpi(void);
 #endif /* LCD_DPI */
 
+#ifdef FB_DOUBLEBUF
+extern int doublebuf;
+#endif
+
 #endif /* __LCD_H__ */

firmware/target/hosted/agptek/debug-agptek.c

@@ -76,6 +76,10 @@ bool dbg_hw_info(void)
         lcd_putsf(0, line++, "lo: %d", lineout_inserted());
 #endif
 
+#ifdef FB_DOUBLEBUF
+        lcd_putsf(0, line++, "fbdb: %d", doublebuf);
+#endif
+
 #ifdef HAVE_BUTTON_DATA
         uint32_t bdata;
         btn = button_read_device(&bdata);

firmware/target/hosted/lcd-linuxfb.c

@@ -43,7 +43,7 @@ fb_data *framebuffer = NULL; /* global variable, see lcd-target.h */
 
 #ifdef FB_DOUBLEBUF
 static int fb_plane;
-static int doublebuf;
+int doublebuf;
 #else
 #define fb_plane 0
 #endif