Update the 86xx reset sequence to try executing a board-specific reset
function.  If the board-specific reset is not implemented or does not
succeed, then assert #HRESET_REQ.  Using #HRESET_REQ is a more standard
reset procedure than the previous method and allows all board
peripherals to be reset if needed.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>