fix: restore libmpeg

[DanielSant0s]

This PR fixes libmpeg and it's sample code.

Change registers to N32 ABI standards.
Fix $at usage, changing it for $t8 and/or using "use no/at".
Fix sample code primitive offset values.
Restore Assembly source compilation, since the C source doesn't work yet.

[fjtrujy]

Please, @uyjulian, take a look. I remember you were trying to make it work.

Why were you trying to make the C version?
Usually, I prefer to have the C version as it is easy to understand, but watching the ASM code, I see how it is using plenty of ASM instructions that our current GCC version is not emitting isn't?

[DanielSant0s]

Why were you trying to make the C version? Usually, I prefer to have the C version as it is easy to understand, but watching the ASM code, I see how it is using plenty of ASM instructions that our current GCC version is not emitting isn't?

We could keep the ASM code until C version get fixed. In fact it has a different code style and instruction support since quadwords aren't native on the current toolchain

[uyjulian]

The main issue I was having is the site where the sample files were located is no longer up

[DanielSant0s]

The main issue I was having is the site where the sample files were located is no longer up

I did some sample to test it using TMPGEnc, you can get by demuxing a PSS too. So it's actually tested.

[DanielSant0s]

@uyjulian Here's the video file I used to test: Link

[Ziemas]

Do we know if this code was originally decompiled from some known library?

[uyjulian]

SMS or libmpeg, probably

[fjtrujy]

Let's merge it as it is not hurting anyone.
@uyjulian, @DanielSant0s , @Ziemas feel free to improve the existing tests attaching new files if needed, in this way we can keep the feature working in a easier way