Add build flag for forcing single buffer mode

RECOVERY_GRAPHICS_FORCE_SINGLE_BUFFER := true

Change-Id: Id5144ea772c3b7ae382b064c41c23acdd0decb84
diff --git a/minuitwrp/graphics_fbdev.cpp b/minuitwrp/graphics_fbdev.cpp
index 3402cba..a1c42d0 100644
--- a/minuitwrp/graphics_fbdev.cpp
+++ b/minuitwrp/graphics_fbdev.cpp
@@ -249,6 +249,7 @@
     }
 
     /* check if we can use double buffering */
+#ifndef RECOVERY_GRAPHICS_FORCE_SINGLE_BUFFER
     if (vi.yres * fi.line_length * 2 <= fi.smem_len) {
         double_buffered = true;
         printf("double buffered\n");
@@ -258,6 +259,10 @@
             gr_framebuffer[0].height * gr_framebuffer[0].row_bytes;
 
     } else {
+#else
+    {
+        printf("RECOVERY_GRAPHICS_FORCE_SINGLE_BUFFER := true\n");
+#endif
         double_buffered = false;
         printf("single buffered\n");
     }