watchdog: octeontx_wdt: Add MIPS Octeon support

This patch adds support for the Marvell Octeon watchdog driver, which
currently only support the ARM64 Octeon TX & TX2 platforms. Since the
IP is pretty similar, it makes sense to extend this driver to also
support the MIPS Octeon SoC.

A follow-up patch will enable this watchdog support on the EBB7304
eval board.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Aaron Williams <awilliams@marvell.com>
Cc: Chandrakala Chavva <cchavva@marvell.com>