kvm: svm: Add SEV feature definitions to KVM

Define the SEV enable bit for the VMCB control structure. The hypervisor
will use this bit to enable SEV in the guest.

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: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: x86@kernel.org
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Borislav Petkov <bp@suse.de>

arch/x86/include/asm/svm.h

@@ -147,6 +147,7 @@ struct __attribute__ ((__packed__)) vmcb_control_area {
 #define SVM_VM_CR_SVM_DIS_MASK  0x0010ULL
 
 #define SVM_NESTED_CTL_NP_ENABLE	BIT(0)
+#define SVM_NESTED_CTL_SEV_ENABLE	BIT(1)
 
 struct __attribute__ ((__packed__)) vmcb_seg {
 	u16 selector;