crashdump: add CONFIG_KEYS dependency

The dm_crypt code fails to build without CONFIG_KEYS:

kernel/crash_dump_dm_crypt.c: In function 'restore_dm_crypt_keys_to_thread_keyring':
kernel/crash_dump_dm_crypt.c:105:9: error: unknown type name 'key_ref_t'; did you mean 'key_ref_put'?

There is a mix of 'select KEYS' and 'depends on KEYS' in Kconfig,
so there is no single obvious solution here, but generally using 'depends on'
makes more sense and is less likely to cause dependency loops.

Link: https://lkml.kernel.org/r/20250620112140.3396316-1-arnd@kernel.org
Fixes: 62f17d9 ("crash_dump: retrieve dm crypt keys in kdump kernel")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alexander Graf <graf@amazon.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Coiby Xu <coxu@redhat.com>
Cc: Dave Vasilevsky <dave@vasilevsky.ca>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: arndb

kernel/Kconfig.kexec

@@ -134,6 +134,7 @@ config CRASH_DM_CRYPT
 	depends on KEXEC_FILE
 	depends on CRASH_DUMP
 	depends on DM_CRYPT
+	depends on KEYS
 	help
 	  With this option enabled, user space can intereact with
 	  /sys/kernel/config/crash_dm_crypt_keys to make the dm crypt keys