configs/amarula_vyasa_rk3288: uboot needs pylibfdt

For this platform, u-boot uses dtoc during the build, which needs Python
libfdt. Set the corresponding option TARGET_UBOOT_NEEDS_PYLIBFDT in the
defconfig.

Signed-off-by: Vincent Stehlé <vincent.stehle@laposte.net>
Cc: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

configs/amarula_vyasa_rk3288_defconfig

@@ -13,6 +13,7 @@ BR2_TARGET_UBOOT_CUSTOM_VERSION=y
 BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2017.11"
 BR2_TARGET_UBOOT_BOARD_DEFCONFIG="vyasa-rk3288"
 BR2_TARGET_UBOOT_NEEDS_DTC=y
+BR2_TARGET_UBOOT_NEEDS_PYLIBFDT=y
 BR2_TARGET_UBOOT_NEEDS_OPENSSL=y
 BR2_TARGET_UBOOT_FORMAT_DTB_IMG=y
 BR2_TARGET_UBOOT_SPL=y