sev/i386: Add initial support for SEV-ES

sev/i386: Add initial support for SEV-ES

Provide initial support for SEV-ES. This includes creating a function to
indicate the guest is an SEV-ES guest (which will return false until all
support is in place), performing the proper SEV initialization and
ensuring that the guest CPU state is measured as part of the launch.

Cc: Paolo Bonzini <[email protected]>
Cc: Richard Henderson <[email protected]>
Cc: Eduardo Habkost <[email protected]>
Reviewed-by: Dr. David Alan Gilbert <[email protected]>
Co-developed-by: Jiri Slaby <[email protected]>
Signed-off-by: Jiri Slaby <[email protected]>
Signed-off-by: Tom Lendacky <[email protected]>
Reviewed-by: Venu Busireddy <[email protected]>
Message-Id: <2e6386cbc1ddeaf701547dd5677adf5ddab2b6bd.1611682609[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>