Adapt icon and skin engine to make use of the new 32bit bitmap capabilities.

You can now use 32bit icons in lists and skins
(except album art, but can be added if wanted). The code also shows how
to free the unused alpha channel data if the bitmap doesn't actually contain
such information.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@30939 a1c6a512-1295-4272-9138-f99709370657

apps/gui/skin_engine/skin_parser.c

@@ -1577,6 +1577,8 @@ static int load_skin_bmp(struct wps_data *wps_data, struct bitmap *bitmap, char*
     close(fd);
     if (ret > 0)
     {
+        /* free unused alpha channel, if any */
+        core_shrink(handle, core_get_data(handle), ret);
         return handle;
     }
     else