Added setting of utcb address to l4_thread_control.
This is going to be moved to exchange_registers() since we need to pass
both the utcb physical and virtual address and exregs fits such context
modification better than thread_control.
- Now libl4 has no references to utcb page or shmat etc.
- Pager does not deal with special case utcb page allocation.
It instead allocates a shared page from shm memory pool.
- All tasks working to original standard.
Next:
- Add per-thread utcb allocation from the kernel
- Add larger register file for standard ipc
- Add long ipc (up to 1Kb)
