powerpc/xive: improve debugging macros

Having the CPU identifier in the debug logs is helpful when tracking
issues. Also add some more logging and fix a compile issue in
xive_do_source_eoi().

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>