clk: imx: Remove unused clk based API

Now that the i.MX6 and i.MX7 clock drivers have been switched to clk_hw based,
we can remove the clk based API that is not used by any i.MX clock driver.

The following APIs are going away now:
- imx_clk_busy_divider
- imx_clk_busy_mux
- imx_clk_fixup_divider
- imx_clk_fixup_mux
- imx_clk_mux_ldb
- imx_clk_gate_dis_flags
- imx_clk_gate_flags

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