drivers/mtd/mtd_progmem.c: Add an upper-half driver that can be used with any FLASH library that provides the itnerfaces defined in include/nuttx/progmem.h

CAN: Add a new CAN upper-half interface, can_txready(), that can be used to break deadlock conditions in certain CAN hardware that supports queuing of TX messages

Make coding style more conformant, take description from OpenGroup.org, rename formal parameters to match names used on OpenGroup.org

Work queues: Logic that sets the queued indication and the logic that does the actual queuing must be atomic