powerpc: Turn get/set_hard_smp_proccessor_id into inlines

They don't need to be macros, and having them as inline functions
avoids warnings about unused variables on some configurations when the
argument isn't evaluated.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>