[mm] Missing Checks on `upage_map`

[ppenna]

Description

We are missing the following semantic checks on upage_map:

• [ ] Check for bad page directory
• [ ] Check for bad page frame

Code Snippet

https://github.com/nanvix/microkernel/blob/53d77ca5636287a918ff5c501b6f77070fbb8085/src/kernel/mm/upool/mod.c#L348-L418