soc: renesas: r8a77995-sysc: Cleanups

Minor cleanup of artefacts caused by deriving from r8a7795-sysc.c:
  - Remove unused inclusion of <linux/sys_soc.h>,
  - Make r8a77995_areas[] const.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>