change default chrony.conf on s390x to use STP refclock (RHEL-62844)

Resolves: RHEL-62844

chrony.spec

@@ -86,9 +86,14 @@ test -n "%{vendorzone}"
 # - use our vendor zone (2.*pool.ntp.org names include IPv6 addresses)
 # - enable leapsectz to get TAI-UTC offset and leap seconds from tzdata
 # - use NTP servers from DHCP
+# - on s390x use the STP reference clock instead of the pool
 sed -e 's|^\(pool \)\(pool.ntp.org\)|\12.%{vendorzone}\2|' \
     -e 's|#\(leapsectz\)|\1|' \
     -e 's|^pool.*pool.ntp.org.*|&\n\n# Use NTP servers from DHCP.\nsourcedir /run/chrony-dhcp|' \
+%ifarch s390x
+    -e 's|^pool |#&|' \
+    -e '1s|^|# Use the s390-specific Server Time Protocol (STP) reference clock.\nrefclock PHC /dev/ptp_s390_stcke poll 2\n\n|' \
+%endif
         < examples/chrony.conf.example2 > chrony.conf
 
 touch -r examples/chrony.conf.example2 chrony.conf