ARM i.MX: Add imx_clk_divider_flags and imx_clk_mux_flags

The default is for dividers to set CLK_SET_PARENT_RATE and for muxes to
not set that flag. In the LDB clock tree, we need the opposite, so add
functions to create divider and mux clocks with configurable flags.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>