[ARM] orion5x: Change names of defines for Reset-Out-Mask register

The name of the define for the Reset-Out-Mask register as well as its
bit for the watchdog reset are changed to match the names used for
Kirkwood (which in turn match the processor specification more
closely). There is no functional change.

This patch prepares for adding orion5x_wdt as a platform device to
Kirkwood.

Signed-off-by: Thomas Reitmayr <treitmayr@devbase.at>
Signed-off-by: Nicolas Pitre <nico@marvell.com>