target/ppc: Add new H-CALL shells for in memory table translation

target/ppc: Add new H-CALL shells for in memory table translation

The use of the new in memory tables introduced in ISAv3.00 for translation,
also referred to as process tables, requires the introduction of 3 new
H-CALLs; H_REGISTER_PROCESS_TABLE, H_CLEAN_SLB, and H_INVALIDATE_PID.

Add shells for each of these and register them as the hypercall handlers.
Currently they all log an unimplemented hypercall and return H_FUNCTION.

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
[dwg: Fix style nits]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>