spdm: Implement KeyExchange

BUG=b:335386464
TEST=spdm unittests

Change-Id: I45625b0220c804f629a7aeb754b61ce4c40fd91e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/spdm/+/5465268
Commit-Queue: Howard Yang <hcyang@google.com>
Tested-by: Howard Yang <hcyang@google.com>
Reviewed-by: Vadim Sukhomlinov <sukhomlinov@google.com>
10 files changed