trunks: expect padding-only RSASSA support for cr50

Check vendor ID when determining if padding-only algorithm is supported
for RSASSA signing. Cr50 provides such support (CL:420811, CL:420854),
other vendors don't.
If padding-only algorithm is supported, no need to set Decrypt attribute
for signing keys.

BUG=chrome-os-partner:60967
TEST=1) On a unowned machine with TPM2: corp enroll, login, install
     a network certificate (gECC or GMC), then:
     a) retrieve the public key from the installed certificate
       LIBCHAPS=`ls /usr/lib**/libchaps.so`
       CERTID=`pkcs11-tool --module=$LIBCHAPS --slot=1 --type=cert \
               -O | grep "ID:" | awk '{print $2}'`
       pkcs11-tool --module=$LIBCHAPS --slot=1 --id=$CERTID \
                   --type=cert -r > /tmp/cert
       openssl x509 -inform der -pubkey -noout -in /tmp/cert > /tmp/pub.key
     b) sign a sample text using the private key for the certificate and
        MD5-RSA-PKCS mechanism, not supported by TPM2_Sign command:
       echo "ABCDEF" > /tmp/1.txt
       pkcs11-tool --module=$LIBCHAPS --slot=1 --id=$CERTID --sign \
                 -i /tmp/1.txt -o /tmp/1.sig -m MD5-RSA-PKCS
     c) verify signature:
       openssl dgst -md5 -verify /tmp/pub.key \
                    -signature /tmp/1.sig /tmp/1.txt
     Step (b) should succeed and step (c) should return "Verified OK"
     2) Unit tests.

Change-Id: I1d396d782ef38e53489c49fb5b4f075eb122536e
Reviewed-on: https://chromium-review.googlesource.com/421246
Commit-Ready: Andrey Pronin <apronin@chromium.org>
Tested-by: Andrey Pronin <apronin@chromium.org>
Reviewed-by: Darren Krahn <dkrahn@chromium.org>
3 files changed