sbin: normalize paths using SRCTOP-relative paths or :H when possible

This simplifies make logic/output

MFC after:	1 month
Sponsored by:	Dell EMC Isilon

ggatec/Makefile

@@ -1,6 +1,6 @@
 # $FreeBSD$
 
-.PATH: ${.CURDIR}/../shared
+.PATH: ${.CURDIR:H}/shared
 
 PROG=	ggatec
 MAN=	ggatec.8
@@ -8,7 +8,7 @@ SRCS=	ggatec.c ggate.c
 
 CFLAGS+= -DMAX_SEND_SIZE=32768
 CFLAGS+= -DLIBGEOM
-CFLAGS+= -I${.CURDIR}/../shared
+CFLAGS+= -I${.CURDIR:H}/shared
 
 LIBADD=	geom util pthread
 

ggated/Makefile

@@ -1,6 +1,6 @@
 # $FreeBSD$
 
-.PATH: ${.CURDIR}/../shared
+.PATH: ${.CURDIR:H}/shared
 
 PROG=	ggated
 MAN=	ggated.8
@@ -8,6 +8,6 @@ SRCS=	ggated.c ggate.c
 
 LIBADD=	pthread util
 
-CFLAGS+= -I${.CURDIR}/../shared
+CFLAGS+= -I${.CURDIR:H}/shared
 
 .include <bsd.prog.mk>

ggatel/Makefile

@@ -1,13 +1,13 @@
 # $FreeBSD$
 
-.PATH: ${.CURDIR}/../shared
+.PATH: ${.CURDIR:H}/shared
 
 PROG=	ggatel
 MAN=	ggatel.8
 SRCS=	ggatel.c ggate.c
 
 CFLAGS+= -DLIBGEOM
-CFLAGS+= -I${.CURDIR}/../shared
+CFLAGS+= -I${.CURDIR:H}/shared
 
 LIBADD=	geom util