Tiva: Move GPIIO prototypes out of arch/arm/include/tiva/irq.h to arch/arm/tiva/tiva_gpio.h where they belong

Fix some time value changes; mostly changing greater than 1000000000 to greater than or equal to 1000000000.  From Juha Niskanen

C++: Remove 'using ::timeval' from ctime.  struct timeval was recently move to sys/time.h where it belongs.  Now there are problems when it is referenced in ctime.  Fixed by just removing it from ctime.  Is that correct?  or should ctime include sys/time.h?  Noted by David Sidrane

VFS: The inode unlink method should not be support if operations on the root pseudo-filesystem are disabled.

this makes mkfatfs use fat_dma_alloc() when CONFIG_FAT_DMAMEMORY is
set. This is needed to ensure mkfatfs operates with boards that use
DMA for microSD

From Andrew Tridgell via the PX4/NuttX repository

Tiva: Updated files to allow for ADC triggering by the timer. I’ve cleaned up some parts of the ADC code, too, and fleshed out the PWM triggering ioctl.  From Calvin Maguranis

NSH: The default priority of the network initialization thread should be lower.  It is CPU intensive and can interfere with other operations

Move some useful internal logic from recvfrom.c and udp_callback.c and put them in ip.h where they can be used more generally

Move some useful internal macros from udp_send.c and put them in ip.h where they can be used more generally