arc: Use "-mcpu=archs" instead of deprecated "-marchs" for ARC HS

Newer ARC toolchains don't support "-marchs" option any longer.
Instead "-mcpu=archs" should be used. What's also important older
toiolchains that support ARC HS cores will also happily accept
"-mcpu=archs" so that's a very safe move.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>

arch/arc/config.mk

@@ -43,11 +43,11 @@ PLATFORM_CPPFLAGS += -marcem
 endif
 
 ifdef CONFIG_CPU_ARCHS34
-PLATFORM_CPPFLAGS += -marchs
+PLATFORM_CPPFLAGS += -mcpu=archs
 endif
 
 ifdef CONFIG_CPU_ARCHS38
-PLATFORM_CPPFLAGS += -marchs
+PLATFORM_CPPFLAGS += -mcpu=archs
 endif
 
 PLATFORM_CPPFLAGS += -ffixed-r25 -D__ARC__ -gdwarf-2