watchdog: sp805_wdt depends on ARM

The SP805 driver is only used by the Spear machines, and uses
writel_relaxed, which is not available on all architectures.

The dependency from CONFIG_ARM avoids compilation problems under
randomconfig when CONFIG_ARM_AMBA is enabled for x86 builds.

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>
Acked-by: Giancarlo Asnaghi <giancarlo.asnaghi@st.com>
Signed-off-by: Davide Ciminaghi <ciminaghi@gnudd.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>