configs/freescale_imx8mnevk: uboot needs openssl

configs/freescale_imx8mnevk: uboot needs openssl

This defconfig was recently bumped to NXP BSP lf-6.6.23-2.0.0.

NXP BSP U-Boot version lf-6.6.23-2.0.0 is based on upstream
version 2024.04. This version now requires OpenSSL.

This defconfig is failing in uboot build, with output:

    In file included from tools/imagetool.h:24,
                     from tools/imagetool.c:8:
    include/image.h:1471:12: fatal error: openssl/evp.h: No such file or directory
     1471 | #  include <openssl/evp.h>
          |            ^~~~~~~~~~~~~~~

This commit fixes the issue by adding
BR2_TARGET_UBOOT_NEEDS_OPENSSL=y in the defconfig.

Signed-off-by: Julien Olivain <[email protected]>
Signed-off-by: Thomas Petazzoni <[email protected]>