configs/pine64: U-Boot needs pylibfdt

Since the bump of U-Boot to 2019.01, pylibfdt is needed to be able to
build the U-Boot image, so we need to enable
BR2_TARGET_UBOOT_NEEDS_PYLIBFDT.

Fixes:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/199339518

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

configs/pine64_defconfig

@@ -20,6 +20,7 @@ BR2_TARGET_UBOOT_CUSTOM_VERSION=y
 BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2019.01"
 BR2_TARGET_UBOOT_BOARD_DEFCONFIG="pine64_plus"
 BR2_TARGET_UBOOT_NEEDS_DTC=y
+BR2_TARGET_UBOOT_NEEDS_PYLIBFDT=y
 BR2_TARGET_UBOOT_NEEDS_ATF_BL31=y
 BR2_TARGET_UBOOT_FORMAT_CUSTOM=y
 BR2_TARGET_UBOOT_FORMAT_CUSTOM_NAME="u-boot.itb"