clk: imx8mp: Add i.MX8MP Dummy clk

i.MX8MP SDHC use CLK_IMX8MP_DUMMY clk entry. Without the clk, the bulk
api will return failure.

The correct entry should be replaced with IMX8MP_IPG_ROOT clk in device
tree. This will be done in Kernel device tree and sync to U-Boot in
future:
https://lore.kernel.org/all/20241012025221.1728438-1-peng.fan@oss.nxp.com/



Fixes: 76332fae ("mmc: fsl_esdhc_imx: Enable AHB/IPG clk with clk bulk API")
Reported-by: Gilles Talis <gilles.talis@nxp.com>
Tested-by: Gilles TALIS <gilles.talis@gmail.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>