build: Consolidate sev_snp feature usage

Since igvm is a required feature of sev_snp and also sev_snp is x86-64
only the cfg attributes at build time can be consolidated & simplified.

Signed-off-by: Rob Bradford <rbradford@meta.com>

cloud-hypervisor/tests/integration_cvm.rs

@@ -10,7 +10,7 @@
 #![allow(dead_code)]
 mod common;
 
-#[cfg(all(feature = "sev_snp", target_arch = "x86_64"))]
+#[cfg(feature = "sev_snp")]
 mod common_cvm {
     use block::ImageType;
     use common::tests_wrappers::*;