mm: x86: Invoke hypercall when page encryption status is changed

Invoke a hypercall when a memory region is changed from encrypted ->
decrypted and vice versa. Hypervisor needs to know the page encryption
status during the guest migration.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: x86@kernel.org
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Steve Rutherford <srutherford@google.com>
Reviewed-by: Venu Busireddy <venu.busireddy@oracle.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
Message-Id: <0a237d5bb08793916c7790a3e653a2cbe7485761.1629726117.git.ashish.kalra@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>