MLK-17491-39 clk: imx: remove private clk-frac-divider

MLK-17491-39 clk: imx: remove private clk-frac-divider

Kernel already supports fractional divider and we switched to it.
See: drivers/clk/clk-fractional-divider.c
So no need keep our private clk-frac-divider copy now which functions
the same, delete it.

Cc: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Bai Ping <ping.bai@nxp.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>