Move drivers/ieee802154 to drivers/wireless/ieee802154; rename include/nuttx/net ieee802154 to 6lowpan.h

sched: Recent change of ASSERT to DEBUGASSERT causes a crash when debug is diabled because there is a critical function call within the assertion

FAT: Add a new configuration option to decouple the logic that retries the direct transfer from the logic that enables DMA memory allocators.

FAT: Add an option to force all transfers to be performed indirectly through the FAT file system's internal sector buffers

Add a CPU affinity set to the TCB if SMP is enable and use this CPU set as a mask for determining which CPUs the thread may run on. Add an affinity field to the attrributes to permit controlling which CPUs a pthread may run on.  Implements pthread_att_setaffinity_np() and pthread_attr_getaffinity_np().

Rename cpuset_t to cpu_set_t which is the type used in some non-standard Linux/GNU interfaces.  Move definitions of cpu_set_t to include/sys/types.h.  Add prototypes for sched_setaffinity(), sched_getaffinity(), pthread_attr_setaffinity_np(), pthread_attr_getaffinity_np(), pthread_setaffinity_np(), and pthread_getaffinity_np().  No implementation is yet in place.