intel_th: Add SPDX GPL-2.0 header to replace GPLv2 boilerplate

This adds SPDX GPL-2.0 header to the Trace Hub driver and removes the
GPLv2 boilerplate text.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>

intel_th: Add Software Trace Hub driver

Software Trace Hub (STH) is a trace source device in the Intel TH
architecture, it generates data that then goes through the switch into
one or several output ports.

STH collects data from software sources using the stm device class
abstraction.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>