powerpc/kexec: Wait 1s for secondaries to enter OPAL

Always include a timeout when waiting for secondary cpus to enter OPAL
in the kexec path, rather than only when crashing.

Signed-off-by: Samuel Mendoza-Jonas <sam.mj@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>