powerpc: Enable CONFIG_CRASH_DUMP=y for ppc64_defconfig

It pulls in more code, including causing us to build a relocatable
kernel, which is good for testing.

The resulting kernel is still usable as a non-crash dump kernel.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/configs/ppc64_defconfig

@@ -50,6 +50,7 @@ CONFIG_HZ_100=y
 CONFIG_BINFMT_MISC=m
 CONFIG_PPC_TRANSACTIONAL_MEM=y
 CONFIG_KEXEC=y
+CONFIG_CRASH_DUMP=y
 CONFIG_IRQ_ALL_CPUS=y
 CONFIG_MEMORY_HOTREMOVE=y
 CONFIG_SCHED_SMT=y