Hello Peter,
Processor Expert development team has provided the following workaround:
Add the Init_SIM component into the project and select the SDHC0_CLKIN pin in the RMII clock source property (in the Component Inspector), see below:

Please note, that there is incorrect signal name of the ENET_1588_CLKIN signal but the selection of the SDHC0_CLKIN ensures that the RMIISRC bit (SOPT2 register) will be set to 1.
In the Component Inspector window of the PinSettings component, select the ENET tab and select the PTE26 pin in the ENET TS clock input selection property, see below:

This selection ensures routing of the PTE26 pin as the ENET_1588_CLKIN pin, i.e. there will be generated the following code:
/* Affects PORTE_PCR26 register */
PORT_HAL_SetMuxMode(PORTE,26UL,kPortMuxAlt2);
Please note that the RMII EXTAL - External reference clock property (on ENET tab of the PinSettings) cannot be used because the Init_ENET already define value of this property (allocation of the pin).
Best Regards,
Marek Neuzil