1. Using X86_FEATURE_ARCH_CAPABILITIES to enumerate the existence of
MSR_IA32_ARCH_CAPABILITIES to avoid using rdmsrl_safe().

2. Since kvm_get_arch_capabilities() is only used in this file, making
it static.
Signed-off-by: NXiaoyao Li <xiaoyao.li@linux.intel.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>