Do not start and stop idle ticking within the timer interrupt
routine, but do it around the whole Lx_kit scheduling, which
is always called when Linux code gets active again, either
because of backend signals, interrupts, or timing signals.
This commit implicitly reverts the (incomplete) solution of
issue #4550
Ref genodelabs/genode#4778
Until now, the lx_emul layer addressed a 5.11 Linux Kernel port,
now that we add new architectures it is better to update the default version
first. There are especially changes in the task_struct code,
and the signature of some functions in the paging subsystem changed.
Ref genodelabs/genode#4411
The re-newed approach currently supports ARM 64-bit only.
It depends on the Platform API of the ARM architecture.
It tries to meet the original semantic of the Linux kernel
functions as far as possible. To achieve this, device drivers
using this library should reference the original Linux kernel
headers at foremost. Only the headers in `src/include/lx_emul/shadow`
have to shadow clone the original ones.
Fix#4225
