crypto: ccp: Implement SEV_PDH_GEN ioctl command

crypto: ccp: Implement SEV_PDH_GEN ioctl command

The SEV_PDH_GEN command is used to re-generate the Platform
Diffie-Hellman (PDH) key. The command is defined in SEV spec section
5.6.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Gary Hook <gary.hook@amd.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: linux-crypto@vger.kernel.org
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
Acked-by: Gary R Hook <gary.hook@amd.com>