Use INCS for non-sys/ libnvpair and libzfs_core includes

While nothing was wrong with libnvpair.h, libzfs_core.h was only guarded by
MK_CDDL rather than MK_CDDL && MK_ZFS. Rather than ugl'if'ying
include/Makefile to impose the extra restriction, just move the non-sys/
includes into INCS with the respect lib builds.

This has the added bonus of allowing third party packagers to try and split
these libs out of the FreeBSD-runtime package, if they are so inclined.

The sys/ include was left alone- generally userland libraries shouldn't
install kernel headers.

MFC after:	1 week

cddl/lib/libnvpair/Makefile

@@ -5,6 +5,7 @@
 
 LIB=	nvpair
 
+INCS=	libnvpair.h
 SRCS=	libnvpair.c \
 	nvpair_alloc_system.c \
 	nvpair_json.c \

cddl/lib/libzfs_core/Makefile

@@ -9,6 +9,7 @@
 LIB=	zfs_core
 LIBADD=	nvpair
 
+INCS=	libzfs_core.h
 SRCS=	libzfs_core.c \
 	libzfs_core_compat.c \
 	zfs_ioctl_compat.c

include/Makefile

@@ -246,12 +246,6 @@ copies: .PHONY .META
 	${INSTALL} -C ${TAG_ARGS} -o ${BINOWN} -g ${BINGRP} -m 444 teken.h \
 	    ${SDESTDIR}${INCLUDEDIR}/teken
 .if ${MK_CDDL} != "no"
-	cd ${SRCTOP}/cddl/contrib/opensolaris/lib/libzfs_core/common; \
-	${INSTALL} -C ${TAG_ARGS} -o ${BINOWN} -g ${BINGRP} -m 444 libzfs_core.h \
-	    ${SDESTDIR}${INCLUDEDIR}
-	cd ${SRCTOP}/cddl/contrib/opensolaris/lib/libnvpair; \
-	${INSTALL} -C ${TAG_ARGS} -o ${BINOWN} -g ${BINGRP} -m 444 libnvpair.h \
-	    ${SDESTDIR}${INCLUDEDIR}
 	cd ${SRCTOP}/sys/cddl/contrib/opensolaris/uts/common/sys; \
 	${INSTALL} -C ${TAG_ARGS} -o ${BINOWN} -g ${BINGRP} -m 444 nvpair.h \
 	    ${SDESTDIR}${INCLUDEDIR}/sys