clk: imx: clk-fixup-mux: Switch to clk_hw based API

Switch the imx_clk_fixup_mux function to clk_hw based API, rename
accordingly and add a macro for clk based legacy. a macro for clk
based legacy. This allows us to move closer to a clear split between
consumer and provider clk APIs.

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