Hi Kyle,
As far as I can tell, "machine_kexec" was removed in commit c9486878
(powerpc/kexec: Remove ppc_md.machine_kexec) on Jan 6th, 2011, which
claims that it was not used.
Unfortunately it looks like it *is* used by the mpc85xx kexec()
support (commit f933a41e), added on Jul 21, 2010.
Thanks for the report. Testing a patch now.
Anton