SUNRPC: Make RPCSEC_GSS_KRB5 select CRYPTO instead of depending on it

Make RPCSEC_GSS_KRB5 select CRYPTO instead of depending on it.  This
unblocks the eventual removal of the selection of CRYPTO from NFSD_V4,
which will no longer be needed by nfsd itself due to switching to the
crypto library functions.  But NFSD_V4 selects RPCSEC_GSS_KRB5, which
still needs CRYPTO.  It makes more sense for RPCSEC_GSS_KRB5 to select
CRYPTO itself, like most other kconfig options that need CRYPTO do.

Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Acked-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>