configs/imx6ullevk: select BR2_TARGET_UBOOT_NEEDS_OPENSSL

Select BR2_TARGET_UBOOT_NEEDS_OPENSSL to fix the following build
error:

include/image.h:1178:12: fatal error: openssl/evp.h: No such file or directory
 1178 | #  include <openssl/evp.h>
      |            ^~~~~~~~~~~~~~~

Fixes:
- https://gitlab.com/buildroot.org/buildroot/-/jobs/1915006189
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit d9f72e37bdad345d80a5dd1c12ab7df2396b35b8)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

configs/imx6ullevk_defconfig

@@ -25,6 +25,7 @@ BR2_TARGET_UBOOT_CUSTOM_VERSION=y
 BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2021.10"
 BR2_TARGET_UBOOT_FORMAT_DTB_IMX=y
 BR2_TARGET_UBOOT_NEEDS_DTC=y
+BR2_TARGET_UBOOT_NEEDS_OPENSSL=y
 
 # required tools to create the SD card image
 BR2_PACKAGE_HOST_DOSFSTOOLS=y