PIC32MX/Z: Partial review of PIC32MZ cp0 register -- need to do more; Also found issues with definitions for PIC32MX -- need to be retested

PIC32MZ: Add file for GPIO interrupt support.  There are issues so configuration is EXPERIMENTAL for now

Extend the fd_set type definition so that it can handle more than 32 descriptors (if so configured).  From Max Neklyudov

Fix places where the errno value was being overwritten by subsequent actions so that the returned errno value was incorrect.  From Max Neklyudov.

PIC32MZ: Add beginnings of CPU initialization logic.  Still some bad logic for setting up peripheral clocking

fs/aio: Corrrect some backward tests in aio_read() and aio_write(): Socket descriptors have higher numbers than file descriptors.  In aio_contain(),  Copy u.ptr (void *) when initializing aioc and not the case specific u.aioc_filep.  From Michal Ulianko.