Makefile ports tweaks cleanup etc

See merge request !211

Fix save games for a custom mod not saving to custom home folder

See merge request !209

Doing this way because I have no idea if the GP2X port was SUPPOSED to use SDL or not in the first place

Removed all support for Dreamcast, XBox, PSP, PS3, GP2X, Wii, and WinCE from files in the sdl/ folder. If you wanted these ports, use the SDL 1.2 code in sdl12

Also removed GP2X setup from sdl/MakeNIX.cfg, use sdl12 for that too

I think it was originally included for defining the "USEASM" macro, but USEASM isn't used by m_fixed.h/c code anymore

Fixed sdl12/Makefile.cfg and sdl12/(port)/Makefile.cfg and related to refer to sdl12/ subfolders, not sdl/ subfolders