crash, powerpc: default to CRASH_DUMP=n on PPC_BOOK3S_32

Fixes boot failures on 6.9 on PPC_BOOK3S_32 machines using Open Firmware. 
On these machines, the kernel refuses to boot from non-zero
PHYSICAL_START, which occurs when CRASH_DUMP is on.

Since most PPC_BOOK3S_32 machines boot via Open Firmware, it should
default to off for them.  Users booting via some other mechanism can still
turn it on explicitly.

Does not change the default on any other architectures for the
time being.

Link: https://lkml.kernel.org/r/20240917163720.1644584-1-dave@vasilevsky.ca


Fixes: 75bc255a ("crash: clean up kdump related config items")
Signed-off-by: Dave Vasilevsky <dave@vasilevsky.ca>
Reported-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
Closes: https://lists.debian.org/debian-powerpc/2024/07/msg00001.html


Acked-by: Michael Ellerman <mpe@ellerman.id.au>	[powerpc]
Acked-by: Baoquan He <bhe@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>