packages: Move powerd to its own package

Nearly everyone wants powerd to manage CPU frequency scaling on real
hardware, even if -utilities isn't installed.  Conversely, very small
jails might want -utilities but don't need powerd.

Move it to its own package and add it to the minimal set.

MFC after:	1 day
Reviewed by:	manu, imp
Differential Revision:	https://reviews.freebsd.org/D52645

libexec/rc/rc.d/Makefile

@@ -50,7 +50,6 @@ CONFS=	DAEMON \
 	${_nscd} \
 	${_opensm} \
 	os-release \
-	powerd \
 	pppoed \
 	pwcheck \
 	quota \
@@ -127,6 +126,10 @@ CONFGROUPS+=		NEWSYSLOG
 NEWSYSLOG=		newsyslog
 NEWSYSLOGPACKAGE=	newsyslog
 
+CONFGROUPS+=		POWERD
+POWERD=			powerd
+POWERDPACKAGE=		powerd
+
 CONFGROUPS+=		SYSLOGD
 SYSLOGD=		syslogd
 SYSLOGDPACKAGE=		syslogd