powerpc/ps3: Add macro PS3_VERBOSE_RESULT

To allow more control of the verbosity of ps3_result() add a check
for the preprocessor macro PS3_VERBOSE_RESULT that builds a verbose
verion of the ps3_result() routine.

Signed-off-by: Geoff Levand <geoff@infradead.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>