sandbox: enable FIT cipher support in defconfig

Linux distributions generally use the "make defconfig && make tools-all"
recipe to generate a uboot-tools (or similar) package.

This patch enables FIT cipher support in the default mkimage build.
Signed-off-by: NPatrick Oppenlander <patrick.oppenlander@gmail.com>

configs/sandbox_defconfig

@@ -8,6 +8,7 @@ CONFIG_DEBUG_UART=y
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_FIT=y
 CONFIG_FIT_SIGNATURE=y
+CONFIG_FIT_CIPHER=y
 CONFIG_FIT_ENABLE_RSASSA_PSS_SUPPORT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_BOOTSTAGE=y