[bsp][synopsys] add the support of synopsys arc emsk

* the initial support of synopsys designware arc processor
* the initial support of synospsy ARC EM Starter Kit
* the bsp code is based on embarc which is a common SDK for
all synopsys ARC-based boards
* use "scons --gdb" to debug emsk with em9d configuration
* for detailed board information, pls go embarc.org

Signed-off-by: Wayne Ren <wei.ren@synopsys.com>

libcpu/arc/em/SConscript

@@ -0,0 +1,17 @@
+# RT-Thread building script for component
+
+from building import *
+
+Import('rtconfig')
+
+cwd     = GetCurrentDir()
+src     = Glob('*.c')
+CPPPATH = [cwd]
+
+
+if rtconfig.PLATFORM == 'gcc':
+    src += Glob('*_gcc.S')
+
+group = DefineGroup('cpu', src, depend = [''], CPPPATH = CPPPATH)
+
+Return('group')