tee: indicate privileged dev in gen_caps

Mirrors the TEE_DESC_PRIVILEGED bit of struct tee_desc:flags into struct
tee_ioctl_version_data:gen_caps as TEE_GEN_CAP_PRIVILEGED in
tee_ioctl_version()

Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>