【修改】class目录修改，合并操作

Signed-off-by: liuxianliang <liuxianliang@rt-thread.com>

SConscript

@@ -7,18 +7,15 @@ src += Glob('samples/ppp_sample.c')
 
 # Air720
 if GetDepend(['PPP_DEVICE_USING_AIR720']):
-    path += [cwd + '/class/air720']
-    src += Glob('class/air720/ppp_device_air720.c')
+    src += Glob('class/ppp_device_air720.c')
 
 # M6312
 if GetDepend(['PPP_DEVICE_USING_M6312']):
-    path += [cwd + '/class/m6312']
-    src += Glob('class/m6312/ppp_device_m6312.c')
+    src += Glob('class/ppp_device_m6312.c')
 
 # SIM800
 if GetDepend(['PPP_DEVICE_USING_SIM800']):
-    path += [cwd + '/class/sim800']
-    src += Glob('class/sim800/ppp_device_sim800.c')
+    src += Glob('class/ppp_device_sim800.c')
 
 group = DefineGroup('ppp_device', src, depend = ['PKG_USING_PPP_DEVICE'], CPPPATH = path)