MdePkg: Update WSMT (Windows SMM Security Mitigation Table) Docs

The WSMT table ProtectionFlags represent a pinky promise from the
firmware that it will implement various secure processes and features,
but we should know what that pinky promise actually represents with
in-code documentation.

Revise the documentation for the Windows SMM Security Mitigation Table
to include detailed descriptions of the Protection Flags, which are
directly drawn from Microsoft's docs.

Update the stable URL to the latest Microsoft docs for cross reference.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jon Kohler <jon@nutanix.com>