kexec: select CRYPTO from KEXEC_FILE instead of depending on it

All other users of crypto code use 'select' instead of 'depends on', so do
the same thing with KEXEC_FILE for consistency.

In practice this makes very little difference as kernels with kexec
support are very likely to also include some other feature that already
selects both crypto and crypto_sha256, but being consistent here helps for
usability as well as to avoid potential circular dependencies.

This reverts the dependency back to what it was originally before commit
74ca317 ("kexec: create a new config option CONFIG_KEXEC_FILE for
new syscall"), which changed changed it with the comment "This should be
safer as "select" is not recursive", but that appears to have been done in
error, as "select" is indeed recursive, and there are no other
dependencies that prevent CRYPTO_SHA256 from being selected here.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 74ca317 ("kexec: create a new config option CONFIG_KEXEC_FILE for new syscall")
Signed-off-by: Arnd Bergmann <[email protected]>
Reviewed-by: Eric DeVolder <[email protected]>
Tested-by: Eric DeVolder <[email protected]>
Acked-by: Baoquan He <[email protected]>
Cc: Herbert Xu <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Albert Ou <[email protected]>
Cc: Alexander Gordeev <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Conor Dooley <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Palmer Dabbelt <[email protected]>
Cc: Paul Walmsley <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Sven Schnelle <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vasily Gorbik <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: arndb

kernel/Kconfig.kexec

@@ -36,7 +36,8 @@ config KEXEC
 config KEXEC_FILE
 	bool "Enable kexec file based system call"
 	depends on ARCH_SUPPORTS_KEXEC_FILE
-	depends on CRYPTO_SHA256=y || !ARCH_SUPPORTS_KEXEC_PURGATORY
+	select CRYPTO
+	select CRYPTO_SHA256
 	select KEXEC_CORE
 	help
 	  This is new version of kexec system call. This system call is