[NES] Audio speed for PAL ROMs

[sapperlott]

I noticed that the background music for my EU Super Mario Bros. NES ROM was playing way too fast. When I tried with a US ROM, the music was playing at the correct speed.

When I had a look around the source code, I noticed that there is a #ifdef for PAL in nesemu-go/components/nofrendo/nes/nes.h which suggests that switching between NTSC and PAL is a compile time setting for NoFrendo and defaults to NTSC (if there is no PAL #define).

It would be cool if the code could be refactored so that this can be changed at runtime somehow (button combination, config file, ...). If that isn't feasible, it should go into the documentation as a known limitation so that people know to get the NTSC versions of their games if possible.