SAMA5D4-EK: NSH confuration now has FAT/ROMFS, /dev/zero, /dev/random via TRNG, an NSH startup script, and a RAM disk at /tmp

Add support for a network device IOCTL to access PHY registers.  Ioctls only implemented for STM32.  From Lazlo

Move the remaining files from include/nuttx/net/uip to include/nuttx/net; Rename *_internal.h header files in net/ to just *.h

SAMA5D4:  More progress on XDMAC driver (still no complete); Also fixes some critical errors in the SAMA5D3 DMA definitions

Move include/nuttx/net/uip/uip-arch.h to include/nuttx/net/arp.h; rename all uip_arp_ functions to arp_