[64DD, Request] Change 64DD IPL Filename

[paradadf]

Hi and before anything else, thanks for the work on this core!

I'd like to suggest renaming the 64DD Bios file from IPL.n64 to 64DD_IPL.bin to match parallel-n64's, as this is the more common name.

https://github.com/libretro/mupen64plus-libretro-nx/blob/develop/mupen64plus-core/src/main/main.c#L720

[m4xw]

I will think about it