CONFIG_WATCHDOG_RIO is not available for thedefaultarchitecture x86.
Result is shown for architecture 64BIT

RIO Hardware Watchdog support

modulename: riowd.ko

configname: CONFIG_WATCHDOG_RIO

Linux Kernel Configuration
└─>Device Drivers
└─>Watchdog Timer Support
└─>PCI support
└─>RIO Hardware Watchdog support
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
Say Y here to support the hardware watchdog capability on Sun RIO
machines. The watchdog timeout period is normally one minute but
can be changed with a boot-time parameter.

source code: