Memory Initialization File for multiple RAMs

I found a solution :)

In case someone has the same problem here is my solution:

To have a parameter concatenated with a string, it needs to represent the number's ASCII value. Therefore 48 needs to be added to its value. An other thing has to be considered: all chars in a string are represented as 8-bit numbers, therefore the parameter has to be 8 bits wide:

parameter  cpuid = 0;

and

defparam memory.altsyncram_component.init_file = {"mem", 8'd48 + cpuid, ".mif"};

fixed my problem :)