STM32 OTF FS device patches from Petteri Aimonen (patches 0001-0003)

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk/nuttx@5687 42af7a65-404d-4744-a932-0658087f49c3
otgfsdev: removed a DEBUGASSERT() that causes a crash on windows reconnect

when windows reconnects to a ACM device, this assert sometimes
triggered. The case it is looking for is handled further down.
Add missing implementation of O_NONBLOCK for serial writes

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk/nuttx@5755 42af7a65-404d-4744-a932-0658087f49c3