apps/examples/usbstorage can now be built as NSH built-in commands;...

apps/examples/usbstorage can now be built as NSH built-in commands; configs/stm3210e-eval/nsh2 now uses these usb storage commands

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@3812 42af7a65-404d-4744-a932-0658087f49c3