crypto: rsa-pkcs1pad: Allow hash to be optional [ver #2]

The original pkcs1pad implementation allowed to pad/unpad raw RSA
output.  However, this has been taken out in commit:
commit c0d20d22

 ("crypto: rsa-pkcs1pad - Require hash to be present")

This patch restored this ability as it is needed by the asymmetric key
implementation.

Signed-off-by: Denis Kenzior <denkenz@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Marcel Holtmann <marcel@holtmann.org>
Reviewed-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: James Morris <james.morris@microsoft.com>