arm64: dts: renesas: r8a77965-salvator-xs: Add SoC name to file header

Document clearly which SoC this DTS applies to, to distinguish from
Salvator-XS boards equipped with other SoCs.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm64/boot/dts/renesas/r8a77965-salvator-xs.dts

 // SPDX-License-Identifier: GPL-2.0
 /*
- * Device Tree Source for the Salvator-X 2nd version board
+ * Device Tree Source for the Salvator-X 2nd version board with R-Car M3-N
  *
  * Copyright (C) 2017 Renesas Electronics Corp.
  */