CR50: hardware based mod exp may need a final reduce
CR50: hardware based mod exp may need a final reduce

The modexp implementation occasionally produces
a result larger than the modulus, in which case a
single final reduce is required.  The software
based implementation already has this check.

BRANCH=none
BUG=chrome-os-partner:43025,chrome-os-partner:47524
TEST=tpmtest.py passes

Change-Id: I0a830781e2a109963394d0702cbc2ca6457c410c
Signed-off-by: nagendra modadugu <5dc366ddbf8fb5981f46478e8436ef712a08b71b@google.com>
Reviewed-on: https://chromium-review.googlesource.com/357010
Commit-Ready: Nagendra Modadugu <5dc366ddbf8fb5981f46478e8436ef712a08b71b@google.com>
Tested-by: Nagendra Modadugu <5dc366ddbf8fb5981f46478e8436ef712a08b71b@google.com>
Reviewed-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec