SAMV7: Revise timer driver.  SAMA5 has one pid/interrupt per timer/counter; SAMV7 has a pid/interrupt per channel

STM32: CCM procfs is no longer a part of the 'base' procfs entries and can now only be supported via run time registration with CONFIG_FS_PROCFS_REGISTER=y

Change prescaler dynamically to support bigger periods on 16 bits timers

SAMV7:  Add some conditional logic to handle the case where the board has no 32.768KHz crystal installed

include/nuttx/net/netdev.h and several Ethernet drivers in arch/:  Most network drivers to not support statistics.  Those that do only support them when DEBUG is enabled.  Each driver collects an architecture specific set of statistics and there is no mechanism in place to view those statistics.  Thus, the driver feature was mostly useless.  This change standardizes the driver statistics and puts the definition in the common network device structure defined in netdev.h where they can be accessed by network applications.  All Ethernet drivers that collect statistics have been adapted to use these common statistics.