Core: Implement proper %s handling for syscall 117 (0x75)

[F0bes]

This fixes #2865

This makes the syscall iterate through the format string which can be considered "slow" but this syscall is only going to be used for debugging purposes anyways :)

Works with my little crude example program

[F0bes]

For those curious or those who'd like to test, here is how you can use this syscall:

void syscallout(char* passedInA0, ...){
    asm __volatile__(
        "li $v1,0x75 \n"
        "syscall    \n" );
}

The syscall supports up to 7 arguments, the stack is not used

[F0bes]

Verified working on Manjaro Linux x32 and x64 :)

[refractionpcsx2]

What about japanese text? Pretty sure that's the reason it had the ShiftJIS in there

[F0bes]

What about japanese text? Pretty sure that's the reason it had the ShiftJIS in there

Uh oh, I recall that having problems due to encoding. I'll look into it after work.

[F0bes]

Seems to work properly without the ShiftJIS stuff.