Syscalls physical memory

[Orycterope]

• syscall MapMmioRegion
• syscall QueryPhysicalAddress
• moving some memory related functions of libuser in their own mem module
• improving the syscalls macro
• fixing the capabilities macro

[todo]

Kernel mappings must be physically continuous.

Virtual memory is a great thing, it can make a fragmented mapping appear contiguous from the userspace. But unfortunately Horizon does not take advantage of this feature, and allocates its mapping as a single Physical Memory Region.
Its syscalls are based around that fact, and to do a `virt_to_phys(addr)`, you simply need to `query_memory(addr).offset` to get its offset in its mapping, and compute its physical address as `query_physical_address(addr).base + offset`.
This will not work when the mapping is composed of several physical regions, and Horizon drivers will not be expecting that. So for them to work on our kernel, we must renounce using fragmented mappings.
For now `query_physical_address` is providing an additional "offset in physical region" return value, to help KFS drivers doing a virt_to_phys without needing to walk the list of physical regions.

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https://github.com/roblabla42/KFS/blob/63f3be7c3ce5eeb8eb0ad7de60c63c0964d264bb/kernel/src/interrupts/syscalls.rs#L120-L130

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This comment was generated by todo based on a TODO comment in 63f3be7 in #201. cc @Orycterope.

[roblabla]

LGTM 👍

[marysaka]

lgtm 👍

[roblabla]

Cargo test fails.