ARC: HSDK-4xD: add initial board support

Add initial HSDK-4xD board support.
The ARC HS4x/HS4xD Development Kit includes a multicore ARC HS4xD-based
chip that integrates a wide range of interfaces including Ethernet,
HDMI, WiFi, Bluetooth, USB, SDIO, I2C, SPI, UART, I2S, ADC, PWM and
GPIO, as well as a Think Silicon GPU.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
diff --git a/board/synopsys/hsdk/config.mk b/board/synopsys/hsdk/config.mk
index 5ae22fa..1d01ef5 100644
--- a/board/synopsys/hsdk/config.mk
+++ b/board/synopsys/hsdk/config.mk
@@ -2,9 +2,17 @@
 #
 # Copyright (C) 2018 Synopsys, Inc. All rights reserved.
 
+ifdef CONFIG_BOARD_HSDK
 PLATFORM_CPPFLAGS += -mcpu=hs38_linux -mlittle-endian -matomic -mll64 \
                      -mdiv-rem -mswap -mnorm -mmpy-option=9 -mbarrel-shifter \
                      -mfpu=fpud_all
+endif
+
+ifdef CONFIG_BOARD_HSDK_4XD
+PLATFORM_CPPFLAGS += -mcpu=hs4x_rel31 -mlittle-endian -matomic -mll64 \
+                     -mdiv-rem -mswap -mnorm -mmpy-option=9 -mbarrel-shifter \
+                     -mfpu=fpud_all
+endif
 
 bsp-generate: u-boot u-boot.bin
 	$(Q)python3 $(srctree)/board/$(BOARDDIR)/headerize-hsdk.py \