powerpc/cpu: Mark start_secondary_resume() __noreturn

start_secondary_resume() doesn't return.  Annotate it as such.  By
extension this also makes arch_cpu_idle_dead() noreturn.

Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/b6b2141f832d8cd8ade65f190d04b011cda5f9bb.1676358308.git.jpoimboe@kernel.org


Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>