sh: Initial support for SH-X3 prototype board.

This adds initial support for the SH-X3 prototype board.
Only simple logic for the IRQ controller and the heartbeat driver
for now.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>
diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index 617765d..24c3361 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -391,6 +391,10 @@
 	help
 	  Select L-BOX RE2 if configuring for the NTT COMWARE L-BOX RE2.
 
+config SH_X3PROTO
+	bool "SH-X3 Prototype board"
+	depends on CPU_SUBTYPE_SHX3
+
 endmenu
 
 source "arch/sh/boards/renesas/hs7751rvoip/Kconfig"