configs/kontron_bl_imx8mm_defconfig: add missing BR2_TARGET_UBOOT_NEEDS_GNUTLS=y

Fixes:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/2781800747

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

configs/kontron_bl_imx8mm_defconfig

@@ -44,6 +44,7 @@ BR2_TARGET_UBOOT_NEEDS_DTC=y
 BR2_TARGET_UBOOT_NEEDS_PYTHON3=y
 BR2_TARGET_UBOOT_NEEDS_PYLIBFDT=y
 BR2_TARGET_UBOOT_NEEDS_OPENSSL=y
+BR2_TARGET_UBOOT_NEEDS_GNUTLS=y
 BR2_TARGET_UBOOT_NEEDS_ATF_BL31=y
 BR2_TARGET_UBOOT_NEEDS_ATF_BL31_BIN=y
 BR2_TARGET_UBOOT_NEEDS_IMX_FIRMWARE=y