platform/x86: mlx-platform: Add definitions for new registers

Add definitions for new registers:
- CPLD3 version - next generation systems are equipped with three CPLD;
- Two reset cause registers, which store the system reset reason (like
  system failures, upgrade failures and so on;

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>