clk: imx: Rename clk-composite clock to clk-composite-7ulp

clk: imx: Rename clk-composite clock to clk-composite-7ulp

The imx/clk-composite is only used by 7ulp. It makes more sense
to mention that in the name of the file and the register function
since later imx-composite clocks may be added.

Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Reviewed-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Arulpandiyan Vadivel <arulpandiyan_vadivel@mentor.com>