mx6: tbs2910: Minimise libfdt code size

This board appears to be very near its size limit and cannot accept the
new checking code in libfdt. Disable this code so this the board can
continue to build.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/tbs2910_defconfig b/configs/tbs2910_defconfig
index ba29b71..2cb5743 100644
--- a/configs/tbs2910_defconfig
+++ b/configs/tbs2910_defconfig
@@ -80,4 +80,5 @@
 CONFIG_I2C_EDID=y
 CONFIG_VIDEO_IPUV3=y
 CONFIG_VIDEO=y
+CONFIG_OF_LIBFDT_ASSUME_MASK=0xff
 # CONFIG_EFI_LOADER is not set