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