powerpc: Provide a separate handler for each IPI action

With the new generic smp call function helpers, I noticed the code in
smp_message_recv was a single function call in many cases.  While
getting the message number from the ipi data is easy, we can reduce
the path length by a function and data-dependent switch by registering
seperate IPI actions for these simple calls.

Originally I left the ipi action array exposed, but then I realized the
registration code should be common too.

The three users each had their own name array, so I made a fourth
to convert all users to use a common one.

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>