clk: imx: clk-pllv3: Use readl_relaxed_poll_timeout() for PLL lock wait

Use readl_relaxed_poll_timeout() for PLL lock wait which can simplify the
code a lot.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Abel Vesa <abel.vesa@nxp.com>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>