arm: add initial skeleton for arm platform support

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>

src/CMakeLists.txt

@@ -23,6 +23,11 @@ if (X86PLAT)
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DX86PLAT=1")
 endif()
 
+if (ARMPLAT)
+  add_subdirectory(arm)
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DARMPLAT=1")
+endif()
+
 set (mraa_LIB_SRCS
   ${mraa_LIB_SRCS_NOAUTO}
 # autogenerated version file