rtc: rtc-spear: Add clk_{un}prepare() support

clk_{un}prepare is mandatory for platforms using common clock framework.
Because for SPEAr we don't do anything in clk_{un}prepare() calls, just
call them once in probe/remove.

Signed-off-by: Deepak Sikri <deepak.sikri@st.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>