clk: samsung: Add set_rate() clk_ops for PLL35xx

This patch add set_rate() and round_rate() for PLL35xx

Reviewed-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Yadwinder Singh Brar <yadi.brar@samsung.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>