This patch introduces the functions 'affinity' and 'num_cpus' to the CPU
session interface. The interface extension will allow the assignment of
individual threads to CPUs. At this point, it is just a stub with no
actual platform support.
The kernel distinguishes local from global IDs by looking at the lowest
6 bits of the thread ID (i.e., in 'L4_ThreadControl'). If those bits are
zero, the ID is interpreted as a local ID. Because those zero bits
overlap with the version bits of global IDs, this invariant could be
violated once the version of a global ID reaches 64. In this case,
'L4_ThreadControl' will return an error on the attempt to create a new
PD. To prevent this from happening, we always set the lowest bit to 1.
