KVM: x86: Check INVPCID feature bit in EBX of leaf 7

Checks and operations on the INVPCID feature bit should use EBX
of CPUID leaf 7 instead of ECX.

Signed-off-by: Junjie Mao <junjie.mao@intel.com>
Signed-off-by: Yongjie Ren <yongjien.ren@intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>