uboot-imx

net: Fix compile errors when SNTP enabled and not DATE

When SNTP is enabled and DATE is not, to_tm() is not built in. It could
be defined when TIMESTAMP is defined, so check for that.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Acked-by: Simon Glass <sjg@chromium.org>