watchdog: tango: rename ARCH_TANGOX to ARCH_TANGO

This change was requested by arm-soc maintainer Kevin Hilman
because the X in TANGOX is a wildcard.

Signed-off-by: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
Acked-by: Mans Rullgard <mans@mansr.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>