ARC: use -mcpu=XXX instead of obsolete -mXXX

-mXXX option is deprecated already in arc-2016.03 toolchain
and removed completely starting from arc-2016.09.

Direct replacement is -mcpu=XXX which is already supported by
arc-2016.03 used today in Lede.

With that change we'll be ready for ARC toolchain update still
keeping everything working with current tools.

Signed-off-by: Alexey Brodkin <Alexey.Brodkin@synopsys.com>
Cc: John Crispin <john@phrozen.org>

include/target.mk

@@ -215,8 +215,8 @@ ifeq ($(DUMP),1)
   ifeq ($(ARCH),arc)
     CPU_TYPE ?= arc700
     CPU_CFLAGS += -matomic
-    CPU_CFLAGS_arc700 = -marc700
-    CPU_CFLAGS_archs = -marchs
+    CPU_CFLAGS_arc700 = -mcpu=arc700
+    CPU_CFLAGS_archs = -mcpu=archs
   endif
   DEFAULT_CFLAGS=$(strip $(CPU_CFLAGS) $(CPU_CFLAGS_$(CPU_TYPE)) $(CPU_CFLAGS_$(CPU_SUBTYPE)))