crypto: testmgr - add an option to disable cryptoalgos' self-tests

By default, CONFIG_CRYPTO_MANAGER_TESTS will be enabled and thus
self-tests will still run, but it is now possible to disable them
to gain some time during bootup.

Signed-off-by: Alexander Shishkin <virtuoso@slind.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>