s390/cert_store: select CRYPTO_LIB_SHA256

A build failure was reported when sha256() is not present:

gcc-13.1.0-nolibc/s390-linux/bin/s390-linux-ld: arch/s390/kernel/cert_store.o: in function `check_certificate_hash':
arch/s390/kernel/cert_store.c:267: undefined reference to `sha256'

Therefore make CONFIG_CERT_STORE select CRYPTO_LIB_SHA256.

Fixes: 8cf57d7 ("s390: add support for user-defined certificates")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Closes: https://lore.kernel.org/all/8ecb57fb-4560-bdfc-9e55-63e3b0937132@infradead.org/
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20230728100430.1567328-1-svens@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

Author: svens-s390

arch/s390/Kconfig

@@ -516,6 +516,7 @@ config KEXEC_SIG
 config CERT_STORE
 	bool "Get user certificates via DIAG320"
 	depends on KEYS
+	select CRYPTO_LIB_SHA256
 	help
 	  Enable this option if you want to access user-provided secure boot
 	  certificates via DIAG 0x320.