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/[email protected]
Fixes: 62f17d9 ("crash_dump: retrieve dm crypt keys in kdump kernel")
Signed-off-by: Arnd Bergmann <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Coiby Xu <[email protected]>
Cc: Dave Vasilevsky <[email protected]>
Cc: Eric Biggers <[email protected]>
Cc: Michael Ellerman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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