Allow DTrace to be compiled-in to the kernel.

This will require for AArch64 as we dont have modules yet.

Sponsored by:	HEIF5
Sponsored by:	ARM Ltd.
Differential Revision:	https://reviews.freebsd.org/D1997

sys/arm/conf/NOTES

@@ -86,3 +86,26 @@ nodevice	cxgbe
 nodevice	pcii
 nodevice	snd_cmi
 nodevice	tnt4882
+
+#
+# Enable the kernel DTrace hooks which are required to load the DTrace
+# kernel modules.
+#
+options 	KDTRACE_HOOKS
+
+# DTrace core
+# NOTE: introduces CDDL-licensed components into the kernel
+#device		dtrace
+
+# DTrace modules
+#device		dtrace_lockstat
+#device		dtrace_profile
+#device		dtrace_sdt
+#device		dtrace_fbt
+#device		dtrace_systrace
+#device		dtrace_prototype
+#device		dtnfscl
+#device		dtmalloc
+
+# Alternatively include all the DTrace modules
+#device		dtraceall