fix: spinlock alignement issue in aarch64 causing so3 to crash

[AndreCostaaa]

This PR aims to fix #141

I first tried to make the lock inside spinlock_t a uint64_t and reordering the mutex arguments but that didn't work. I believe the problem is within the pcb_t struct which causes the misalignment.
I tried putting the __attribute__((aligned(8))) inside the pcb_t structure but that didn't help.

So, I took it a step further and decided to put pcb mutex list in the heap so we can align it by calling as we control how the memory is aligned in the heap

I also took the liberty to:

1. Decrease the amount of mutexes per pcb
2. Make the mutex_lock/unlock syscalls more robust by actually checking the mutex id instead of just indexing inside the list

[daniel-rossier]

hmm. bad naming of arguments -> please use syscall_args instead of a

[daniel-rossier]

So, the do_mutex_lock() takes an id as argument instead of the lock. How is it managed? How is the link between the mutex and the ID handled?
[UPDATE] We leave as it is today since we will have a clean implementation of mutex as soon as we are able to support the full MUSL library.

[AndreCostaaa]

Sounds reasonable. Will revert the change :)