i386: kvm: set CPUID_EXT_HYPERVISOR on kvm_arch_get_supported_cpuid()

Full grep for kvm_arch_get_supported_cpuid:

   kvm.h:uint32_t kvm_arch_get_supported_cpuid(KVMState *env, uint32_t function,
   target-i386/cpu.c:        x86_cpu_def->cpuid_7_0_ebx_features = kvm_arch_get_supported_cpuid(kvm_state, 0x7, 0, R_EBX);
   target-i386/cpu.c:            *eax = kvm_arch_get_supported_cpuid(s, 0xA, count, R_EAX);
   target-i386/cpu.c:            *ebx = kvm_arch_get_supported_cpuid(s, 0xA, count, R_EBX);
   target-i386/cpu.c:            *ecx = kvm_arch_get_supported_cpuid(s, 0xA, count, R_ECX);
   target-i386/cpu.c:            *edx = kvm_arch_get_supported_cpuid(s, 0xA, count, R_EDX);
   target-i386/cpu.c:            *eax = kvm_arch_get_supported_cpuid(s, 0xd, count, R_EAX);
   target-i386/cpu.c:            *ebx = kvm_arch_get_supported_cpuid(s, 0xd, count, R_EBX);
   target-i386/cpu.c:            *ecx = kvm_arch_get_supported_cpuid(s, 0xd, count, R_ECX);
   target-i386/cpu.c:            *edx = kvm_arch_get_supported_cpuid(s, 0xd, count, R_EDX);
   target-i386/kvm.c:uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
   target-i386/kvm.c:        cpuid_1_edx = kvm_arch_get_supported_cpuid(s, 1, 0, R_EDX);
   target-i386/kvm.c:    env->cpuid_features &= kvm_arch_get_supported_cpuid(s, 1, 0, R_EDX);
 * target-i386/kvm.c:    env->cpuid_ext_features &= kvm_arch_get_supported_cpuid(s, 1, 0, R_ECX);
   target-i386/kvm.c:    env->cpuid_ext2_features &= kvm_arch_get_supported_cpuid(s, 0x80000001,
   target-i386/kvm.c:    env->cpuid_ext3_features &= kvm_arch_get_supported_cpuid(s, 0x80000001,
   target-i386/kvm.c:    env->cpuid_svm_features  &= kvm_arch_get_supported_cpuid(s, 0x8000000A,
   target-i386/kvm.c:        kvm_arch_get_supported_cpuid(s, KVM_CPUID_FEATURES, 0, R_EAX);
   target-i386/kvm.c:            kvm_arch_get_supported_cpuid(s, 0xC0000001, 0, R_EDX);

Note that there is only one call for CPUID[1].ECX above (*), and it is
the one that gets hacked to include CPUID_EXT_HYPERVISOR, so we can
simply make kvm_arch_get_supported_cpuid() set it, to let the rest of
the code automatically know that the flag can be safely set by QEMU.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
