HSI: hsi_char: Add HSI char device kernel configuration

Add HSI character device kernel configuration

Signed-off-by: Andras Domokos <andras.domokos@nokia.com>
Signed-off-by: Carlos Chinea <carlos.chinea@nokia.com>
diff --git a/drivers/hsi/Kconfig b/drivers/hsi/Kconfig
index 937062e..d94e38d 100644
--- a/drivers/hsi/Kconfig
+++ b/drivers/hsi/Kconfig
@@ -14,4 +14,6 @@
 	bool
 	default y
 
+source "drivers/hsi/clients/Kconfig"
+
 endif # HSI