xhci: fix unsafe memory usage in xhci tracing

commit cbf286e8

 upstream.

Removes static char buffer usage in the following decode functions:
	xhci_decode_trb()
	xhci_decode_ptortsc()

Caller must provide a buffer to use.
In tracing use __get_str() as recommended to pass buffer.

Minor chanes are needed in xhci debugfs code as these functions are also
used there. Changes include moving XHCI_MSG_MAX definititon from
xhci-trace.h to xhci.h

Cc: <stable@vger.kernel.org>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20210820123503.2605901-2-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>