Add configuration of NTP

* default to one server: 'ntp'

recipes-conf/ntp/files/ntp.conf

+# /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for help
+
+driftfile /var/lib/ntp/ntp.drift
+
+# You do need to talk to an NTP server or two (or three).
+server ntp
+
+# pool.ntp.org maps to about 1000 low-stratum NTP servers.  Your server will
+# pick a different set every time it starts up.  Please consider joining the
+# pool: <http://www.pool.ntp.org/join.html>
+#server 0.debian.pool.ntp.org iburst
+#server 1.debian.pool.ntp.org iburst
+#server 2.debian.pool.ntp.org iburst
+#server 3.debian.pool.ntp.org iburst
+

recipes-conf/ntp/ntp_%.bbappend

+FILESEXTRAPATHS_prepend := "${THISDIR}/files:"