ARC: HSDK-4xD: use separate config file

HSDK-4xD has quite different environment so let's split
HSDK and HSDK-4xD configs file.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
diff --git a/board/synopsys/hsdk/MAINTAINERS b/board/synopsys/hsdk/MAINTAINERS
index d385951..73f71fd 100644
--- a/board/synopsys/hsdk/MAINTAINERS
+++ b/board/synopsys/hsdk/MAINTAINERS
@@ -4,3 +4,5 @@
 F:	board/synopsys/hsdk/
 F:	configs/hsdk_defconfig
 F:	configs/hsdk_4xd_defconfig
+F:	include/configs/hsdk-4xd.h
+F:	include/configs/hsdk.h