target-i386: Eliminate CONFIG_KVM #ifdefs

The compiler is already able to eliminate the kvm_arch_get_supported_cpuid()
calls in kvm_cpu_fill_host() and filter_features_for_kvm(), so we can
eliminate the CONFIG_KVM #ifdefs there.

Also, kvm_cpu_fill_host() and host_cpuid() don't need to check
CONFIG_KVM, as they don't have any KVM-specific function calls.

Tested to build successfully with CONFIG_KVM disabled, using the
following CFLAGS combinations: "-DNDEBUG", "-DNDEBUG -O', "-DNDEBUG
-O0", "-DNDEBUG -O1", "-DNDEBUG -O2".

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
