Implement syscall support

* Finally we can start executing some kernel functions now. Executing
syscalls is very straightforward; just create an exception of type 8
and the handler will handle the rest. This is the first time the exception
handler is used on the EE so I'm bit anxious whether it will be bug free.

* Log each syscall and print its name instead of just a simple number. Known
syscalls along with their ids are on ps2devwiki [1]

[1] https://playstationdev.wiki/ps2devwiki/index.php?title=Syscalls