soc: apple: rtkit: Do not copy the reg state structure to the stack

The register state struct is 848 bytes, which ends up bloating the
apple_rtkit_crashlog_dump_regs stack frame beyond 1024 on some
32-bit platforms, triggering compile warnings.

This doesn't matter for 64BIT/ARM64, but there's also no good reason to
copy the structure to the stack in this case. We can use __packed to
avoid alignment issues, there are no double-read hazards, and this is a
fatal error path so performance does not matter.

Fixes: 22991d8d ("soc: apple: rtkit: Add register dump decoding to crashlog")
Signed-off-by: Asahi Lina <lina@asahilina.net>
Reviewed-by: Eric Curtin <ecurtin@redhat.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>