Merge branch 'kvm-sev-init2' into HEAD

The idea that no parameter would ever be necessary when enabling SEV or
SEV-ES for a VM was decidedly optimistic.  The first source of variability
that was encountered is the desired set of VMSA features, as that affects
the measurement of the VM's initial state and cannot be changed
arbitrarily by the hypervisor.

This series adds all the APIs that are needed to customize the features,
with room for future enhancements:

- a new /dev/kvm device attribute to retrieve the set of supported
  features (right now, only debug swap)

- a new sub-operation for KVM_MEM_ENCRYPT_OP that can take a struct,
  replacing the existing KVM_SEV_INIT and KVM_SEV_ES_INIT

It then puts the new op to work by including the VMSA features as a field
of the The existing KVM_SEV_INIT and KVM_SEV_ES_INIT use the full set of
supported VMSA features for backwards compatibility; but I am considering
also making them use zero as the feature mask, and will gladly adjust the
patches if so requested.

In order to avoid creating *two* new KVM_MEM_ENCRYPT_OPs, I decided that
I could as well make SEV and SEV-ES use VM types.  This allows SEV-SNP
to reuse the KVM_SEV_INIT2 ioctl.

And while at it, KVM_SEV_INIT2 also includes two bugfixes.  First of all,
SEV-ES VM, when created with the new VM type instead of KVM_SEV_ES_INIT,
reject KVM_GET_REGS/KVM_SET_REGS and friends on the vCPU file descriptor
once the VMSA has been encrypted...  which is how the API should have
always behaved.  Second, they also synchronize the FPU and AVX state.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>