generic loader does not do virtual to physical address translation when loading MIPS ELF
Description of problem:

Steps to reproduce:
1.build two ELFs, whose virtual address is at kseg0<p>
2.load one ELF with generic loader "-device loader,file=test1.elf", the other ELF with "-kernel test2.elf"<p>
3.generic loader loads test1.elf without doing address translation, while mipssim load_kernel will do that with cpu_mips_kseg0_to_phys<p>
Additional information:
generic_loader_realize calls load_elf_as with the argument translate_fn=NULL. Maybe, we can set translate_fn when elf_machine is EM_MIPS.