x86/cpufeatures: Enable/unmask SEV-SNP CPU feature

With all the required host changes in place, it should now be possible
to initialize SNP-related MSR bits, set up RMP table enforcement, and
initialize SNP support in firmware while maintaining legacy support for
SEV/SEV-ES guests. Go ahead and enable the SNP feature now.

Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240126041126.1927228-23-michael.roth@amd.com

arch/x86/include/asm/disabled-features.h

@@ -117,7 +117,11 @@
 #define DISABLE_IBT	(1 << (X86_FEATURE_IBT & 31))
 #endif
 
+#ifdef CONFIG_KVM_AMD_SEV
+#define DISABLE_SEV_SNP		0
+#else
 #define DISABLE_SEV_SNP		(1 << (X86_FEATURE_SEV_SNP & 31))
+#endif
 
 /*
  * Make sure to add features to the correct mask