powerpc/rtas: complete ibm,suspend-me status codes

We don't completely account for the possible return codes for
ibm,suspend-me. Add definitions for these.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201207215200.1785968-3-nathanl@linux.ibm.com