Trivial: style fix

make the style checker happy

Fix licenses

Add dependency on muslcsys and remove duplication of syscalls

libsel4camkes previously had its own implementations of all muslc syscalls. These
syscalls were originally copied from libsel4muslcsys and modified / added to.

This change modifies the syscalls in the following ways
* Syscalls that were completely duplicated have been removed in favour of the
muslcsys ones
* Some of the IO syscalls were extended in CAmkES and the run time overriding
is used to provide the extended behaviour and fall back to the libsel4muslcsys
implementation for the remaining behaviour
* exit, thread and related syscalls are completely overriden in favour of CAmkES ones
* memory related syscalls (brk, mmap, munmap, etc) are removed in favour of
libsel4muslcsys ones. The ability for CAmkES to control the heap allocation is now
dependent upon libsel4muslcsys havings its heap set to 0 so that it switches into
dynamic mode, at which point CAmkES can install its own heap
* Remaining syscalls are not present in libsel4muslcsys and their implementation
is left unchanged
All syscalls have their names changed to have a camkes_ prefix to prevent symbol
name clashes
This change removes any duplicate syscalls, and uses the run time overriding of
syscalls to extend the IO syscalls

libsel4camkes: Implement gettid using the TLS thread index.

This gives component instances a more accurate idea of their thread ID. Note
that thread IDs are not currently used for anything interesting in the subset of
Musl C's functionality that we use.

libsel4camkes: Implement getppid.

libsel4camkes: Implement a more complete getpid.

This commit alters the `getpid` implementation to now return a component
instance index. This has the effect of giving each component instance a distinct
PID.

Move all code from libsel4muslccamkes into libsel4camkes.

This commit consolidates all the code from these libraries into libsel4camkes.
The boundary between these libraries has been increasingly blurred, and
currently neither can be used without the other. Future planned changes
introduce further complex dependencies between them and it was seen to be
advantageous to just collapse both into a single library. Current directory
structure should leave all legacy projects unimpacted by this commit.

JIRA: CAMKES-513