ARC: rework setting of ARC CPU specific compiler options

It's a very rare if at all existing occasion when ARC CPU template
is used as is w/o any changes - in the end it's a beauty and competitive
advantage of ARC cores to be tailored for a particular use-case - and
so it doesn't make a lot of sense to offer template-based "-mcpu" selection.
Given for each and every platform we end-up adding quite a few more flags
it's logical to move "-mcpu" selection to platform's definition as well
which we exactly do here.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
diff --git a/board/synopsys/nsim/config.mk b/board/synopsys/nsim/config.mk
new file mode 100644
index 0000000..40f9578
--- /dev/null
+++ b/board/synopsys/nsim/config.mk
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0+
+#
+# Copyright (C) 2020 Synopsys, Inc. All rights reserved.
+
+# CONFIG_NSIM_BOARD_CPPFLAGS is a string variable which comes from defconfig
+# with double quotes. We use echo to remove them so CONFIG_NSIM_BOARD_CPPFLAGS
+# won't be treated by compiler as a single option.
+PLATFORM_CPPFLAGS += $(shell echo $(CONFIG_NSIM_BOARD_CPPFLAGS))