Add Syscalls module

[andressbarajas]

Here we are again but with a more slimmed down PR.

1. Pulled all the syscall calls to its own module (syscalls.h, syscall.c, syscall_font.s). New syscall to get Dreamcast ID.
2. Updated Cdrom, Flashrom, and BioFonts to use this new module.

Tested on GDEMU using raster_melt, and custom example for biosfont. Havent tested flashrom but if the other syscalls work then I expect the flashrom ones to work too since they use the same code to make the system call.

Ive decided to look into DCLOAD syscalls at a later date.

[andressbarajas]

I believe this PR is Ready to GO! To summarize:

1. No behavior change. I centralized all the system calls into syscalls.h/.c, syscall_font.s.
2. New syscalls to get Dreamcast ID, Dreamcast system icons, soft reset the console, exit to CD menu.

[gyrovorbis]

I am approving this to let people know that I have reviewed it, tested that it builds, looked at Doxygen, and no longer feel I have anything to contribute or need from it; HOWEVER, it's too big for me to feel comfortable merging without @ljsebald.

Also, @QuzarDC and @DC-SWAT, did you have anything else to add?

[DC-SWAT]

Looks good for me.

[QuzarDC]

Fantastic work! Totally inline with my #151 project of standardization. And with them all laid out like this we now have easy access to some undocumented/unused ones to explore.

Had one change request of a typo that was my fault to begin with (and left some extra comments for future work but that don't require any change). Then it's good to go.