aarch64: init serial port by parsing dtb file

See merge request redox-os/kernel!241

Set relocation-model=static

Closes #107

See merge request redox-os/kernel!240

Replace #[thread_local]

See merge request redox-os/kernel!239

Demand paging

See merge request redox-os/kernel!238

Since these are stored in arrays that are typically 512 KiB each
(i.e. which in turn typically store metadata for 128 MiB), they will
certainly be a page-size multiple, and large contiguous allocations are
allowed at least at boot time. Not only is the linked-list allocator
less efficient for that, but this change will also help reduce TLB
overhead.