arch: Add compatibility check for CPUID.0x7.0x1:ECX

Register ECX of CPUID leaf 0x7 sub-leaf 0x1 (Structured Extended Feature
Enumeration Sub-leaf) is currently not checked, but it should be.

KVM exposes bit 5 (MSR_IMM: the immediate forms of the RDMSR and WRMSR
instructions) when the host does.

Live migrating from a source that supports MSR_IMM to a destination
that does not is not safe.

Signed-off-by: Oliver Anderson <oliver.anderson@cyberus-technology.de>
On-behalf-of: SAP oliver.anderson@sap.com

arch/src/x86_64/mod.rs

@@ -451,6 +451,12 @@ impl CpuidFeatureEntry {
                 feature_reg: CpuidReg::EAX,
                 compatible_check: CpuidCompatibleCheck::BitwiseSubset,
             },
+            CpuidFeatureEntry {
+                function: 7,
+                index: 1,
+                feature_reg: CpuidReg::ECX,
+                compatible_check: CpuidCompatibleCheck::BitwiseSubset,
+            },
             // Leaf 0x8000_0001, ECX/EDX, CPUID features bits
             CpuidFeatureEntry {
                 function: 0x8000_0001,