clk: imx8mp: Remove the none exist pcie clocks

In the i.MX8MP PCIe design, the PCIe PHY REF clock comes from external
OSC or internal system PLL. It is configured in the IOMUX_GPR14 register
directly, and can't be contolled by CCM at all.
Remove the PCIE PHY clock from clock driver to clean up codes.
There is only one PCIe in i.MX8MP, remove the none exist second PCIe
related clocks.
Remove the none exsits clocks IDs together.

Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Reviewed-by: Jason Liu <jason.hui.liu@nxp.com>
Signed-off-by: Abel Vesa <abel.vesa@nxp.com>