get rid of HAL pixelformats 5551 and 4444

Change-Id: I39409103144c1ba09078c4ddc323a58987fb09ea
diff --git a/include/ui/PixelFormat.h b/include/ui/PixelFormat.h
index d06728b..627cfb6 100644
--- a/include/ui/PixelFormat.h
+++ b/include/ui/PixelFormat.h
@@ -61,8 +61,8 @@
     PIXEL_FORMAT_RGB_888     = HAL_PIXEL_FORMAT_RGB_888,    // 3x8-bit RGB
     PIXEL_FORMAT_RGB_565     = HAL_PIXEL_FORMAT_RGB_565,    // 16-bit RGB
     PIXEL_FORMAT_BGRA_8888   = HAL_PIXEL_FORMAT_BGRA_8888,  // 4x8-bit BGRA
-    PIXEL_FORMAT_RGBA_5551   = HAL_PIXEL_FORMAT_RGBA_5551,  // 16-bit ARGB
-    PIXEL_FORMAT_RGBA_4444   = HAL_PIXEL_FORMAT_RGBA_4444,  // 16-bit ARGB
+    PIXEL_FORMAT_RGBA_5551   = 6,                           // 16-bit ARGB
+    PIXEL_FORMAT_RGBA_4444   = 7,                           // 16-bit ARGB
 };
 
 typedef int32_t PixelFormat;