Use MK_SSP=no after including bsd.own.mk to disable SSP instead of user-knob

WITH[OUT]_SSP to avoid hitting an error if user has WITH_SSP in their
make.conf. Ports now use this knob.

  make[7]: "/usr/src/share/mk/bsd.own.mk" line 466: WITH_SSP and
  WITHOUT_SSP can't both be set.

This is similar to previous cleanup done in r188895

Approved by:	bapt
Reviewed by:	jlh (earlier version)
Approved by:	re (marius)
MFC after:	1 week

sys/boot/i386/efi/Makefile

@@ -1,10 +1,10 @@
 # $FreeBSD$
 
 NO_MAN=
-WITHOUT_SSP=
 BUILDING_EFI=
 
 .include <bsd.own.mk>
+MK_SSP=		no
 
 PROG=		loader.sym
 INTERNALPROG=

sys/boot/powerpc/boot1.chrp/Makefile

@@ -1,6 +1,6 @@
 # $FreeBSD$
 
-WITHOUT_SSP=
+SSP_CFLAGS=
 
 PROG=           boot1.elf
 NEWVERSWHAT=    "Open Firmware boot block" ${MACHINE_ARCH}

sys/boot/userboot/libstand/Makefile

@@ -6,10 +6,10 @@
 #   quite large.
 #
 
-WITHOUT_SSP=
 NO_MAN=
 
 .include <bsd.own.mk>
+MK_SSP=		no
 
 S=		${.CURDIR}/../../../../lib/libstand
 

sys/boot/userboot/test/Makefile

@@ -2,9 +2,9 @@
 
 
 NO_MAN=
-WITHOUT_SSP=
 
 .include <bsd.own.mk>
+MK_SSP=		no
 
 PROG=		test
 INTERNALPROG=

sys/boot/userboot/userboot/Makefile

@@ -1,9 +1,9 @@
 # $FreeBSD$
 
 NO_MAN=
-WITHOUT_SSP=
 
 .include <bsd.own.mk>
+MK_SSP=		no
 
 SHLIB_NAME=	userboot.so
 NO_CTF=		yes