[libcpu] fix the cacheflush issue when lwP is not enable

libcpu/arm/cortex-a/cache.c

@@ -123,6 +123,7 @@ rt_base_t rt_hw_cpu_dcache_status(void)
     return 0;
 }
 
+#ifdef RT_USING_LWP
 #define ICACHE (1<<0)
 #define DCACHE (1<<1)
 #define BCACHE (ICACHE|DCACHE)
@@ -143,3 +144,4 @@ int sys_cacheflush(void *addr, int size, int cache)
     }
     return -1;
 }
+#endif