target-i386: Add "filtered-features" property to X86CPU

This property will contain all the features that were removed from the
CPU because they are not supported by the host.

This way, libvirt or other management tools can emulate the
check/enforce behavior by checking if filtered-properties is all zeroes,
before starting the guest.

Example output where some features were missing:

  $ qemu-system-x86_64 -enable-kvm -cpu Haswell,check -S \
    -qmp unix:/tmp/m,server,nowait
  warning: host doesn't support requested feature: CPUID.01H:ECX.fma [bit 12]
  warning: host doesn't support requested feature: CPUID.01H:ECX.movbe [bit 22]
  warning: host doesn't support requested feature: CPUID.01H:ECX.tsc-deadline [bit 24]
  warning: host doesn't support requested feature: CPUID.01H:ECX.xsave [bit 26]
  warning: host doesn't support requested feature: CPUID.01H:ECX.avx [bit 28]
  warning: host doesn't support requested feature: CPUID.07H:EBX.fsgsbase [bit 0]
  warning: host doesn't support requested feature: CPUID.07H:EBX.bmi1 [bit 3]
  warning: host doesn't support requested feature: CPUID.07H:EBX.hle [bit 4]
  warning: host doesn't support requested feature: CPUID.07H:EBX.avx2 [bit 5]
  warning: host doesn't support requested feature: CPUID.07H:EBX.smep [bit 7]
  warning: host doesn't support requested feature: CPUID.07H:EBX.bmi2 [bit 8]
  warning: host doesn't support requested feature: CPUID.07H:EBX.erms [bit 9]
  warning: host doesn't support requested feature: CPUID.07H:EBX.invpcid [bit 10]
  warning: host doesn't support requested feature: CPUID.07H:EBX.rtm [bit 11]
  [...]
  $ ./QMP/qmp --path=/tmp/m \
    qom-get --path=/machine/icc-bridge/icc/child[0] \
            --property=filtered-features
  item[0].cpuid-register: EDX
  item[0].cpuid-input-eax: 2147483658
  item[0].features: 0
  item[1].cpuid-register: EAX
  item[1].cpuid-input-eax: 1073741825
  item[1].features: 0
  item[2].cpuid-register: EDX
  item[2].cpuid-input-eax: 3221225473
  item[2].features: 0
  item[3].cpuid-register: ECX
  item[3].cpuid-input-eax: 2147483649
  item[3].features: 0
  item[4].cpuid-register: EDX
  item[4].cpuid-input-eax: 2147483649
  item[4].features: 0
  item[5].cpuid-register: EBX
  item[5].cpuid-input-eax: 7
  item[5].features: 4025
  item[5].cpuid-input-ecx: 0
  item[6].cpuid-register: ECX
  item[6].cpuid-input-eax: 1
  item[6].features: 356519936
  item[7].cpuid-register: EDX
  item[7].cpuid-input-eax: 1
  item[7].features: 0

Example output when no feature is missing:

  $ qemu-system-x86_64 -enable-kvm -cpu Nehalem,enforce -S \
    -qmp unix:/tmp/m,server,nowait
  [...]
  $ ./QMP/qmp --path=/tmp/m \
    qom-get --path=/machine/icc-bridge/icc/child[0] \
            --property=filtered-features
  item[0].cpuid-register: EDX
  item[0].cpuid-input-eax: 2147483658
  item[0].features: 0
  item[1].cpuid-register: EAX
  item[1].cpuid-input-eax: 1073741825
  item[1].features: 0
  item[2].cpuid-register: EDX
  item[2].cpuid-input-eax: 3221225473
  item[2].features: 0
  item[3].cpuid-register: ECX
  item[3].cpuid-input-eax: 2147483649
  item[3].features: 0
  item[4].cpuid-register: EDX
  item[4].cpuid-input-eax: 2147483649
  item[4].features: 0
  item[5].cpuid-register: EBX
  item[5].cpuid-input-eax: 7
  item[5].features: 0
  item[5].cpuid-input-ecx: 0
  item[6].cpuid-register: ECX
  item[6].cpuid-input-eax: 1
  item[6].features: 0
  item[7].cpuid-register: EDX
  item[7].cpuid-input-eax: 1
  item[7].features: 0

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
