Use sel4runtime for TLS management.

sel4runtime will initilise the TLS for the first thread in the process
(this should not be overridden as it was in entry.c).

Instead of using the nasty trick of de-initialising the TLS with a null
pointer to set variables in remote TLS, we use the tools from
sel4runtime that aren't so destructive to configure the state for libbmk
and to also ensure that the IPC buffer pointer is set on each thread.

The existing tooling for creating and allocating TLS can still be used
as sel4runtime makes no assumptions or changes to the size or layout of
TLS.

THe platform-independant interface for configuring the TLS from
sel4runtime is also used rather than specific implementations for
different architectures.

Update copyright year to 2018 for new/significantly updated files

Add ARM TLS, clock and platform code