创建，添加sdram

rt-thread/components/drivers/rtc/SConscript

@@ -0,0 +1,18 @@
+from building import *
+
+cwd = GetCurrentDir()
+src = []
+
+CPPPATH = [cwd + '/../include']
+group = []
+
+if GetDepend(['RT_USING_RTC']):
+    src = src + ['rtc.c']
+    if GetDepend(['RT_USING_ALARM']):
+        src = src + ['alarm.c']
+    if GetDepend(['RT_USING_SOFT_RTC']):
+        src = src + ['soft_rtc.c']
+
+group = DefineGroup('DeviceDrivers', src, depend = ['RT_USING_RTC'], CPPPATH = CPPPATH)
+
+Return('group')