clk: clk-private: Add DEFINE_CLK macro

All macros used for creating different kind of clocks have similar code for
initializing struct clk. This patch removes those redundant lines and create
another macro DEFINE_CLK.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>