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

SAMA5: FIQs should be disabled along with IRQs on most exeptions in most configuratinons.  arm_decodefiq and arm_decodeirq are mutually exclusive and, hence, can use the same interrupt stack

SAMA5D4:  Add support for secure/FIQ interrupts; SAIC supports need to be be enabled unconditionally

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

SAMA5D4: Initial XDMAC driver logic; initial check-in is little more the the DMAC driver with some name changes

SAMA5D3/4:  More renaming.  Change SAMA5D3 EMAC to EMACA and SAMA5D4 to EMACB so that the configuration and build system can configure them.  I might come up with something better later