Support MMAP and MUNMAP system calls

[joergroedel]

This PR implements the MMAP and MUNMAP system calls and foundations for MRESIZE. The system calls do not have Posix semantics yet. In fact, partial unmaps are not supported. A VMM can only be unmapped as a whole for now.

The foundations for MRESIZE are also implemented, but that support is not finished yet. Therefore this PR is marked as Draft.

[n-ramacciotti]

With None (Anonymous mapping) here 0 is assigned and it is later used in kernel/src/syscall/class0.rs:

pub fn sys_mmap(
..
let opt = obj_get(obj_id.into()).ok();
let mmap_addr = if let Some(obj) = opt {
 //map with obj
}else{
 //anonymous mapping
}
..

But obj_id 0 is already used in kernel/src/task/tasks.rs:

fn task_attach_console() {
    let file_handle = stdout_open();
    let obj_handle = ObjHandle::new(0);
    current_task()
        .add_obj_at(file_handle, obj_handle)
        .expect("Failed to attach console");
}

So, sys_mmap finds something when looking for object 0 and it enters the wrong branch.

Workaround for testing with coconut-alloc

Changing obj_id to another value (like 1) makes the mmap work correctly when testing in the userspace allocator PR.

This in syscall/src/console.rs should be changed as well:

static CONSOLE_HANDLE: FsObjHandle = FsObjHandle::new(ObjHandle::new(0));