sha2 digest on ppc

[Barbier, Renaud]

Commit 03fb5524b06 has changed the configuration selection for hash algorithm. For instance:

-config SHA256
+config HAVE_DIGEST_SHA256
 	Bool

This breaks on my PPC platform as the configuration selection has not been changed in crypto/sha2.c
if (!IS_ENABLED(CONFIG_SHA256))

Still working on my ARM platform because the algo is registered somewhere else (arch/arm/crypto/sha256_glue.c)

RENAUD: sha256_digest_register
RENAUD: sha256_digest_register: ALGO NOT REGISTERED
...
RENAUD: digest_algo_get_by_name: sha256 sha256
RENAUD: digest_algo_get_by_name: sha224 sha256
RENAUD: digest_algo_get_by_name: md5 sha256
FIT: /images/kernel-1/hash-1: hash OK