ARM: rmobile: salvator-x: Add R8A7796 support

Add minor ifdeffery and default board config for the Salvator-XS board
with R8A7796 M3 SoC.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@renesas.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
diff --git a/board/renesas/salvator-x/MAINTAINERS b/board/renesas/salvator-x/MAINTAINERS
index 33c105d..f7b98fb 100644
--- a/board/renesas/salvator-x/MAINTAINERS
+++ b/board/renesas/salvator-x/MAINTAINERS
@@ -4,3 +4,4 @@
 F:	board/renesas/salvator-x/
 F:	include/configs/salvator-x.h
 F:	configs/r8a7795_salvator-x_defconfig
+F:	configs/r8a7796_salvator-x_defconfig