powerpc/85xx: fix compile error without CONFIG_CRASH_DUMP

powerpc/85xx: fix compile error without CONFIG_CRASH_DUMP

Since commit 5c4233cc0920 ("powerpc/kdump: Split KEXEC_CORE and
CRASH_DUMP dependency"), crashing_cpu is not available without
CONFIG_CRASH_DUMP. Fix compile error on 64-BIT 85xx owing to this
change.

Fixes: 5c4233cc0920 ("powerpc/kdump: Split KEXEC_CORE and CRASH_DUMP dependency")
Cc: stable@vger.kernel.org # v6.9+
Reported-by: Christian Zigotzky <chzigotzky@xenosoft.de>
Closes: https://lore.kernel.org/all/fa247ae4-5825-4dbe-a737-d93b7ab4d4b9@xenosoft.de/
Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240510080757.560159-1-hbathini@linux.ibm.com