sev: update sev-inject-launch-secret to make gpa optional

sev: update sev-inject-launch-secret to make gpa optional

If the gpa isn't specified, it's value is extracted from the OVMF
properties table located below the reset vector (and if this doesn't
exist, an error is returned).  OVMF has defined the GUID for the SEV
secret area as 4c2eb361-7d9b-4cc3-8081-127c90d3d294 and the format of
the <data> is: <base>|<size> where both are uint32_t.  We extract
<base> and use it as the gpa for the injection.

Note: it is expected that the injected secret will also be GUID
described but since qemu can't interpret it, the format is left
undefined here.

Signed-off-by: James Bottomley <jejb@linux.ibm.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20210204193939.16617-3-jejb@linux.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>