Can I understand that the external clock sources which is written in your datasheet of i.MX8M(IMX8MDQLQCEC Rev.1, 3.1.4 External clock sources) are referred to the following pins?
CCM_EXT_CLK1 GPIO1_IO00 ALT6
CCM_EXT_CLK2 GPIO1_IO01 ALT6
CCM_EXT_CLK3 GPIO1_IO06 ALT6
CCM_EXT_CLK4 GPIO1_IO07 ALT6
(From RM, IMX8MDQLQRM, Rev.0, 18.104.22.168 Muxing Options)