sev/i386: register the guest memory range which may contain encrypted data

sev/i386: register the guest memory range which may contain encrypted data

When SEV is enabled, the hardware encryption engine uses a tweak such
that the two identical plaintext at different location will have a
different ciphertexts. So swapping or moving a ciphertexts of two guest
pages will not result in plaintexts being swapped. Hence relocating
a physical backing pages of the SEV guest will require some additional
steps in KVM driver. The KVM_MEMORY_ENCRYPT_{UN,}REG_REGION ioctl can be
used to register/unregister the guest memory region which may contain the
encrypted data. KVM driver will internally handle the relocating physical
backing pages of registered memory regions.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>