SPEAr: Switch to common clock framework

SPEAr SoCs used its own clock framework since now. From now on they will move to
use common clock framework.

This patch updates existing SPEAr machine support to adapt for common clock
framework.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Reviewed-by: Mike Turquette <mturquette@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>