Revert "crypto: pkcs7 - remove sha1 support"

This reverts commit 16ab7cb5 because it
broke iwd.  iwd uses the KEYCTL_PKEY_* UAPIs via its dependency libell,
and apparently it is relying on SHA-1 signature support.  These UAPIs
are fairly obscure, and their documentation does not mention which
algorithms they support.  iwd really should be using a properly
supported userspace crypto library instead.  Regardless, since something
broke we have to revert the change.

It may be possible that some parts of this commit can be reinstated
without breaking iwd (e.g. probably the removal of MODULE_SIG_SHA1), but
for now this just does a full revert to get things working again.

Reported-by: Karel Balej <balejk@matfyz.cz>
Closes: https://lore.kernel.org/r/CZSHRUIJ4RKL.34T4EASV5DNJM@matfyz.cz


Cc: Dimitri John Ledkov <dimitri.ledkov@canonical.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Tested-by: Karel Balej <balejk@matfyz.cz>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>