configs/imx8mpevk: select BR2_TARGET_UBOOT_NEEDS_OPENSSL

Select BR2_TARGET_UBOOT_NEEDS_OPENSSL to fix the following build
error:

include/image.h:1394:12: fatal error: openssl/evp.h: No such file or directory
 1394 | #  include <openssl/evp.h>

Fixes: https://gitlab.com/buildroot.org/buildroot/-/jobs/5858180070
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Tested-By: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

configs/freescale_imx8mpevk_defconfig

@@ -29,6 +29,7 @@ BR2_TARGET_UBOOT_CUSTOM_TARBALL_LOCATION="$(call github,nxp-imx,uboot-imx,lf-6.1
 BR2_TARGET_UBOOT_BOARD_DEFCONFIG="imx8mp_evk"
 BR2_TARGET_UBOOT_CONFIG_FRAGMENT_FILES="board/freescale/imx8mpevk/uboot-fragment.config"
 BR2_TARGET_UBOOT_NEEDS_DTC=y
+BR2_TARGET_UBOOT_NEEDS_OPENSSL=y
 BR2_TARGET_UBOOT_NEEDS_UTIL_LINUX=y
 BR2_TARGET_UBOOT_NEEDS_GNUTLS=y
 BR2_TARGET_UBOOT_FORMAT_CUSTOM=y