thunderbolt.4: Initial manual for HW Relnotes

This manual contains nothing and is only suitable for the HW Relnotes,
but lets get it in so we have something and then can iterate on it.

MFC after:		3 minutes
Fixes:			2ed9833791 (thunderbolt: Import USB4 code)
Discussed with:		obiwac
Differential Revision:	https://reviews.freebsd.org/D52847

share/man/man4/Makefile

@@ -589,6 +589,7 @@ MAN=	aac.4 \
 	tdfx.4 \
 	termios.4 \
 	textdump.4 \
+	thunderbolt.4 \
 	ti.4 \
 	timecounters.4 \
 	tmpfs.4 \

share/man/man4/thunderbolt.4

@@ -0,0 +1,22 @@
+.\"
+.\" Copyright (c) 2025 Alexander Ziaee
+.\"
+.\" SPDX-License-Identifier: BSD-2-Clause
+.\"
+.Dd October 2, 2025
+.Dt THUNDERBOLT 4
+.Os
+.Sh NAME
+.Nm thunderbolt
+.Nd USB4 controller driver
+.Sh SYNOPSIS
+.Cd device thunderbolt
+.Sh HARDWARE
+The
+.Nm
+driver supports USB4 controllers.
+.Sh HISTORY
+The
+.Nm
+driver appeared in
+.Fx 15.0 .