KVM: x86: Add a struct to consolidate host values, e.g. EFER, XCR0, etc...

KVM: x86: Add a struct to consolidate host values, e.g. EFER, XCR0, etc...

Add "struct kvm_host_values kvm_host" to hold the various host values
that KVM snapshots during initialization.  Bundling the host values into
a single struct simplifies adding new MSRs and other features with host
state/values that KVM cares about, and provides a one-stop shop.  E.g.
adding a new value requires one line, whereas tracking each value
individual often requires three: declaration, definition, and export.

No functional change intended.

Link: https://lore.kernel.org/r/20240423221521.2923759-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>