PSP-2000/3000 : Attempt to set main memory as 62M

I think may be on real PSP-2000/3000, it is not exactly allocate full 64M though need more testing .It still works fine for HD Remaster game like MH3 HD (Thanks @daniel299)

Also make #2183 better and no more need to switch back to PSP-1000 to run it .