KVM: selftests: Introduce SEV VM type check

KVM: selftests: Introduce SEV VM type check

In preparation for SNP, declutter the vm type check by introducing a
SEV-SNP VM type check as well as a transitive set of helper functions.

The SNP VM type is the subset of SEV-ES. Similarly, the SEV-ES and SNP
types are subset of the SEV VM type check.

Signed-off-by: Pratik R. Sampat <prsampat@amd.com>
Link: https://lore.kernel.org/r/20250305230000.231025-7-prsampat@amd.com
[sean: make the helpers static inlines]
Signed-off-by: Sean Christopherson <seanjc@google.com>